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for example: bibliographic, document-text, statistical. Digital databases are managed using database management systems, which store database contents, allowing data creation and maintenance, and search and other access  (Dell Studio XPS 1640 Battery)  .

Architecture

Database architecture consists of three levels, external, conceptual and internal. Clearly separating the three levels was a major feature of the relational database model that dominates 21st century databases        (Dell Vostro 1710 Battery)  .

The external level defines how users understand the organization of the data. A single database can have any number of views at the external level. The internal level defines how the data is physically stored and processed by the computing system. Internal architecture is concerned with cost, performance, scalability and other operational matters  Dell KM958 battery .

The conceptual is a level of indirection between internal and external. It provides a common view of the database that is uncomplicated by details of how the data is stored or managed, and that can unify the various external views into a coherent whole  Dell Studio 1555 battery .

Database management systems

A database management system (DBMS) consists of software that operates databases, providing storage, access, security, backup and other facilities    Sony VGP-BPS13 battery .

Database management systems can be categorized according to the database model that they support, such as relational or XML, the type(s) of computer they support, such as a server cluster or a mobile phone, the query language(s) that access the database, such as SQL or XQuery, performance trade-offs, such as maximum scale or maximum speed or others   Sony VGP-BPS13/B battery .

Some DBMS cover more than one entry in these categories, e.g., supporting multiple query languages. Examples of some commonly used DBMS are MySQL, PostgreSQL, Microsoft Access, SQL Server, FileMaker,Oracle,Sybase, dBASE, Clipper,FoxPro etc   Sony VGP-BPS13/S battery .

Almost every database software comes with an Open Database Connectivity (ODBC) driver that allows the database to integrate with other databases.

Components of DBMS

Most DBMS as of 2009 implement a relational model          Sony VGP-BPS13A/B battery .

Other DBMS systems, such as Object DBMS, offer specific features for more specialized requirements. Their components are similar, but not identical           Sony VGP-BPS13B/B battery .

RDBMS components

• Sublanguages— Relational DBMS (RDBMS) include Data Definition Language (DDL) for defining the structure of the database, Data Control Language (DCL) for defining security/access controls, and Data Manipulation Language (DML) for querying and updating data      Sony VGP-BPL9 battery .
• Interface drivers—These drivers are code libraries that provide methods to prepare statements, execute statements, fetch results, etc. Examples include ODBC, JDBC, MySQL/PHP,FireBird/Python      Sony VGP-BPS13B/B battery .
• SQL engine—This component interprets and executes the DDL, DCL, and DML statements. It includes three major components (compiler, optimizer, and executor).
• Transaction engine—Ensures that multiple SQL statements either succeed or fail as a group, according to application dictates      Sony VGP-BPL15 battery .
• Relational engine—Relational objects such as Table, Index, and Referential integrity constraints are implemented in this component.
• Storage engine—This component stores and retrieves data from secondary storage, as well as managing transaction commit and rollback, backup and recovery, etc     Dell Inspiron E1505 battery .

ODBMS components

Object DBMS (ODBMS) has transaction and storage components that are analogous to those in an RDBMS. Some DBMS handle DDL, DML and update tasks differently. Instead of using sublanguages, they provide APIs for these purposes   Dell Latitude E6400 battery .

They typically include a sublanguage and accompanying engine for processing queries with interpretive statements analogous to but not the same as SQL. Example object query languages are OQL, LINQ, JDOQL, JPAQL and others. The query engine returns collections of objects instead of relational rows      HP Pavilion dv6000 Battery .

Types

Operational database

These databases store detailed data about the operations of an organization. They are typically organized by subject matter, process relatively high volumes of updates using transactions. Essentially every major organization on earth uses such databases   SONY VAIO VGN-FZ Battery .

Examples include customer databases that record contact, credit, and demographic information about a business' customers, personnel databases that hold information such as salary, benefits, skills data about employees, Enterprise resource planning that record details about product components     SONY VAIO VGN-FZ18 Battery ,

parts inventory, and financial databases that keep track of the organization's money, accounting and financial dealings.

Data warehouse

Data warehouses archive modern data from operational databases and often from external sources such as market research firms  SONY VAIO VGN-FZ21E Battery .

Often operational data undergoes transformation on its way into the warehouse, getting summarized, anonymized, reclassified, etc. The warehouse becomes the central source of data for use by managers and other end-users who may not have access to operational data      SONY VAIO VGN-FW21E Battery .

For example, sales data might be aggregated to weekly totals and converted from internal product codes to use UPC codes so that it can be compared with ACNielsen data.Some basic and essential components of data warehousing include retrieving and analyzing data, transforming,loading and managing data so as to make it available for further use  SONY VAIO VGN-NR11S/S Battery .

Operations in a data warehouse are typically concerned with bulk data manipulation, and as such, it is unusual and inefficient to target individual rows for update, insert or delete. Bulk native loaders for input data and bulk SQL passes for aggregation are the norm  SONY VAIO VGN-NR11M/S Battery .

Analytical database

Analysts may do their work directly against a data warehouse or create a separate analytic database for Online Analytical Processing. For example, a company might extract sales records for analyzing the effectiveness of advertising and other sales promotions at an aggregate level       SONY VAIO VGN-NR11Z/S Battery .

Distributed database

These are databases of local work-groups and departments at regional offices, branch offices, manufacturing plants and other work sites. These databases can include segments of both common operational and common user databases, as well as data generated and used only at a user’s own site       SONY VAIO VGN-NR11Z/T Battery .

End-user database

These databases consist of data developed by individual end-users. Examples of these are collections of documents in spreadsheets, word processing and downloaded files, even managing their personal baseball card collection   Sony VAIO VGN-FZ21E Battery .

External database

These databases contain data collected for use across multiple organizations, either freely or via subscription. The Internet Movie Database is one example      Sony VAIO VGN-FW21E Battery .

Hypermedia databases

The World wide web can be thought of as a database, albeit one spread across millions of independent computing systems. Web browsers "process" this data one page at a time, while web crawlersand other software provide the equivalent of database indexes to support search and other activities    Sony VAIO VGN-NR11S/S Battery .

Models

Post-relational database models

Products offering a more general data model than the relational model are sometimes classified as post-relational.Alternate terms include "hybrid database", "Object-enhanced RDBMS" and others   Sony VAIO VGN-NR11Z/S Battery .

The data model in such products incorporates relations but is not constrained by E.F. Codd's Information Principle, which requires that all information in the database must be cast explicitly in terms of values in relations and in no other way Sony VAIO VGN-NR11M/S Battery .

Some of these extensions to the relational model integrate concepts from technologies that pre-date the relational model. For example, they allow representation of a directed graph with trees on thenodes.

Some post-relational products extend relational systems with non-relational features       Sony VAIO VGN-NR11Z/T Battery .

Others arrived in much the same place by adding relational features to pre-relational systems. Paradoxically, this allows products that are historically pre-relational, such as PICK and MUMPS, to make a plausible claim to be post-relational      SONY VAIO VGN-FZ180E Battery .

Object database models

In recent years, the object-oriented paradigm has been applied in areas such as engineering and spatial databases, telecommunications and in various scientific domains. The conglomeration of object oriented programming and database technology led to this new kind of database       SONY VAIO VGN-FZ220E Battery .

These databases attempt to bring the database world and the application-programming world closer together, in particular by ensuring that the database uses the same type system as the application program. This aims to avoid the overhead (sometimes referred to as the impedance mismatch)        SONY VAIO VGN-FZ340E Battery

of converting information between its representation in the database (for example as rows in tables) and its representation in the application program (typically as objects). At the same time, object databases attempt to introduce key ideas of object programming, such as encapsulation and polymorphism, into the world of databases     SONY VAIO VGN-FZ430E Battery .

A variety of these ways have been tried for storing objects in a database. Some products have approached the problem from the application-programming side, by making the objects manipulated by the program persistent. This also typically requires the addition of some kind of query language      SONY VAIO VGN-FZ460E Battery ,

since conventional programming languages do not provide language-level functionality for finding objects based on their information content. Others have attacked the problem from the database end, by defining an object-oriented data model for the database       SONY VAIO VGN-FZ480E Battery ,

and defining a databaseprogramming language that allows full programming capabilities as well as traditional query facilities..

Storage structures

Databases may store relational tables/indexes in memory or on hard disk in one of many forms        SONY VAIO VGN-FZ4000 Battery:

• ordered/unordered flat files
• ISAM
• heaps
• hash buckets
• logically-blocked files
• B+ trees      SONY VAIO VGN-FZ31E Battery

The most commonly used are B+ trees and ISAM.

Object databases use a range of storage mechanisms. Some use virtual memory-mapped files to make the native language (C++, Java etc.) objects persistent     SONY VAIO VGN-FZ31B Battery .

This can be highly efficient but it can make multi-language access more difficult. Others disassemble objects into fixed- and varying-length components that are then clustered in fixed sized blocks on disk and reassembled into the appropriate format on either the client or server address space       SONY VAIO VGN-FZ31J Battery .

Another popular technique involves storing the objects in tuples (much like a relational database) which the database server then reassembles into objects for the client.

Other techniques include clustering by category (such as grouping data by month, or location), storing pre-computed query results, known as materialized views, partitioning data by range (e.g., a data range) or by hash   SONY VAIO VGN-FZ31M Battery .

Memory management and storage topology can be important design choices for database designers as well. Just as normalization is used to reduce storage requirements and improve database designs, conversely denormalization is often used to reduce join complexity and reduce query execution time     SONY VAIO VGN-FZ31Z Battery .

Indexing

Indexing is a technique for improving database performance. The many types of index share the common property that they eliminate the need to examine every entry when running a query. In large databases, this can reduce query time/cost by orders of magnitude      SONY VAIO VGN-FZ38M Battery .

The simplest form of index is a sorted list of values that can be searched using a binary search with an adjacent reference to the location of the entry, analogous to the index in the back of a book. The same data can have multiple indexes (an employee database could be indexed by last name and hire date    SONY VGP-BPS8 Battery .

Indexes affect performance, but not results. Database designers can add or remove indexes without changing application logic, reducing maintenance costs as the database grows and database usage evolves       SONY VGP-BPS13 Battery .

Given a particular query, the DBMS' query optimizer is responsible for devising the most efficient strategy for finding matching data. The optimizer decides which index or indexes to use, how to combine data from different parts of the database, how to provide data in the order requested, etc     SONY VGP-BPS13/S Battery .

Indexes can speed up data access, but they consume space in the database, and must be updated each time the data is altered. Indexes therefore can speed data access but slow data maintenance. These two properties determine whether a given index is worth the cost     SONY VGP-BPS13A/B Battery .

Transactions

As every software system, a DBMS operates in a faulty computing environment and prone to failures of many kinds. A failure can corrupt the respective database unless special measures are taken to prevent this       SONY VGP-BPS13B/B Battery .

A DBMS achieves certain levels of fault tolerance by encapsulating in database transactions units of work (executed programs) performed upon the respective database      SONY VGP-BPS13A/S Battery .

The ACID rules

Most DBMS provide some form of support for transactions, which allow multiple data items to be updated in a consistent fashion, such that updates that are part of a transaction succeed or fail in unison. The so-called ACID rules, summarized here, characterize this behavior      SONY VGP-BPS13AS Battery :

• Atomicity: Either all the data changes in a transaction must happen, or none of them. The transaction must be completed, or else it must be undone (rolled back).
• Consistency: Every transaction must preserve the declared consistency rules for the database  Dell Inspiron 1320n Battery .
• Isolation: Two concurrent transactions cannot interfere with one another. Intermediate results within one transaction must remain invisible to other transactions. The most extreme form of isolation isserializability, meaning that transactions that take place concurrently could instead be performed in some series, without affecting the ultimate result Dell Inspiron 1464 Battery.
• Durability: Completed transactions cannot be aborted later or their results discarded. They must persist through (for instance) DBMS restarts.

In practice, many DBMSs allow the selective relaxation of these rules to balance perfect behavior with optimum performance  Dell Inspiron 1564 Battery .

Concurrency control and locking

Concurrency control is essential for the correctness of transactions executed concurrently in a DBMS, which is the common execution mode for performance reasons. The main concern and goal of concurrency control is isolation  Dell Inspiron 1764 Battery.

Isolation

Isolation refers to the ability of one transaction to see the results of other transactions. Greater isolation typically reduces performance and/or concurrency, leading DBMSs to provide administrative options to reduce isolation   Dell Studio 1450 Battery .

For example, in a database that analyzes trends rather than looking at low-level detail, increased performance might justify allowing readers to see uncommitted changes ("dirty reads".)

A common way to achieve isolation is by locking      Dell Studio 1457 Battery .

When a transaction modifies a resource, the DBMS stops other transactions from also modifying it, typically by locking it. Locks also provide one method of ensuring that data does not change while a transaction is reading it or even that it doesn't change until a transaction that once read it has completed      Dell Latitude D610 Battery .

Lock types

Locks can be shared or exclusive, and can lock out readers and/or writers. Locks can be created implicitly by the DBMS when a transaction performs an operation, or explicitly at the transaction's request.

Shared locks allow multiple transactions to lock the same resource. The lock persists until all such transactions complete  Toshiba NB100 Battery .

Exclusive locks are held by a single transaction and prevent other transactions from locking the same resource.

Read locks are usually shared, and prevent other transactions from modifying the resource. Write locks are exclusive, and prevent other transactions from modifying the resource    Toshiba Satellite M65 battery .

On some systems, write locks also prevent other transactions from reading the resource.

The DBMS implicitly locks data when it is updated, and may also do so when it is read. Transactions explicitly lock data to ensure that they can complete without complications. Explicit locks may be useful for some administrative tasks   Toshiba Satellite M60 battery .

Locking can significantly affect database performance, especially with large and complex transactions in highly concurrent environments.

Lock granularity

Locks can be coarse, covering an entire database, fine-grained, covering a single data item, or intermediate covering a collection of data such as all the rows in a RDBMS table       Dell Latitude D830 Battery .

Deadlocks

Deadlocks occur when two transactions each require data that the other has already locked exclusively. Deadlock detection is performed by the DBMS, which then aborts one of the transactions and allows the other to complete     Dell Latitude D620 Battery .

Replication

Database replication involves maintaining multiple copies of a database on different computers, to allow more users to access it, or to allow a secondary site to immediately take over if the primary site stops working     Dell Inspiron Mini 10 Battery .

Some DBMS piggyback replication on top of their transaction logging facility, applying the primary's log to the secondary in near real-time. Database clustering is a related concept for handling larger databases and user communities by employing a cluster of multiple computers to host a single database that can use replication as part of its approach  Sony VGN-FW11S Battery .

Security

Database security denotes the system, processes, and procedures that protect a database from unauthorized activity.

DBMSs usually enforce security through access control, auditing, and encryption      Sony VGN-FW11M Battery :

• Access control manages who can connect to the database via authentication and what they can do via authorization.
• Auditing records information about database activity: who, what, when, and possibly where.
• Encryption protects data at the lowest possible level by storing and possibly transmitting data in an unreadable form Sony VGN-FW139E/H battery .
• The DBMS encrypts data when it is added to the database and decrypts it when returning query results. This process can occur on the client side of a network connection to prevent unauthorized access at the point of use        Dell Latitude E5400 Battery .

Confidentiality

Law and regulation governs the release of information from some databases, protecting medical history, driving records, telephone logs, etc         Dell Latitude E4200 Battery .

In the United Kingdom, database privacy regulation falls under the Office of the Information Commissioner. Organizations based in the United Kingdom and holding personal data in digital format such as databases must register with the Office     Dell Inspiron 300M Battery .

A real-time database is a processing system designed to handle workloads whose state is constantly changing (Buchmann). This differs from traditional databases containing persistent data, mostly unaffected by time. For example, a stock market changes very rapidly and is dynamic      Dell Vostro A840 Battery .

The graphs of the different markets appear to be very unstable and yet a database has to keep track of current values for all of the markets of the New York Stock Exchange (Kanitkar). Real-time processing means that a transaction is processed fast enough for the result to come back and be acted on right away (Capron)       Dell Studio 1737 battery .

Real-time databases are useful for accounting, banking, law, medical records, multi-media, process control, reservation systems, and scientific data analysis (Snodgrass). As computers increase in power and can store more data, they are integrating themselves into our society and are employed in many applications      Dell Inspiron E1505 battery .

Overview

Real-time databases are traditional databases that use an extension to give the additional power to yield reliable responses. They use timing constraints that represent a certain range of values for which the data are valid        Dell RM791 battery .

This range is called temporal validity. A conventional database cannot work under these circumstances because the inconsistencies between the real world objects and the data that represents them are too severe for simple modifications. An effective system needs to be able to handle time-sensitive queries, return only temporally valid data, and support priority scheduling  Dell XPS M1530 battery .

To enter the data in the records, often a sensor or an input device monitors the state of the physical system and updates the database with new information to reflect the physical system more accurately (Abbot). When designing a real-time database system, one should consider how to represent valid time, how facts are associated with real-time system   Dell XPS M2010 battery .

Also, consider how to represent attribute values in the database so that process transactions and data consistency have no violations.

When designing a system, it is important to consider what the system should do when deadlines are not met   Acer Aspire One battery.

For example, an air-traffic control system constantly monitors hundreds of aircraft and makes decisions about incoming flight paths and determines the order in which aircraft should land based on data such as fuel, altitude, and speed. If any of this information is late, the result could be devastating     Toshiba Satellite P10 Battery .

To address issues of obsolete data, the timestamp can support transactions by providing clear time references.

Preserving data consistency

Although the real-time database system may seem like a simple system, problems arise during overload when two or more database transactions require access to the same portion of the database       SONY VGN-FZ210CE Battery .

A transaction is usually the result of an execution of a program that accesses or changes the contents of a database (Singhal). A transaction is different from a stream because a stream only allows read-only operations, and transactions can do both read and write operations       Dell Precision M70 Battery .

This means in a stream, multiple users can read from the same piece of data, but they cannot both modify it (Abbot). A database must let only one transaction operate at a time to preserve data consistency. For example, if two students demand to take the remaining spot for a section of a class and they hit submit at the same time, only one student should be able to register for it (Abbot)  Toshiba Satellite L305 Battery .

Real-time databases can process these requests utilizing scheduling algorithms for concurrency control, prioritizing both students’ requests in some way. Throughout this article, we assume that the system has a single processor, a disk based database, and a main memory pool(Haritsa)        Toshiba Satellite T4900 Battery .

In real-time databases, deadlines are formed and different kinds of systems respond differently to data that does not meet its deadline. In a real-time system, each transaction uses a timestamp to schedule the transactions (Abbot)   Toshiba PA3399U-2BRS battery .

A priority mapper unit assigns a level of importance to each transaction upon its arrival in the database system that is dependent on how the system views times and other priorities. The timestamp method on relies on the arrival time in the system. Researchers indicate that for most studies, transactions are sporadic with unpredictable arrival times   Toshiba Satellite A200 Battery .

For example, the system gives an earlier request deadline to a higher priority and a later deadline to a lower priority (Haritsa). Below is a comparison of different scheduling algorithms.

Earliest Deadline

PT = DT — The value of a transaction is not important. An example is a group of people calling to order a product Toshiba Satellite 1200 Battery .

Highest Value

PT = 1/VT — The deadline is not important. Some transactions should get to CPU based on criticalness, not fairness. This is an example of least slack that can wait the least amount of time. If the telephone switchboards were overloaded, people who call 911 should get priority (Snodgrass)     Toshiba Satellite M300 Battery .

Value inflated deadline

PT = DT/VT — Gives equal weight to deadline and values based on scheduling. An example is registering for classes where the student selects a block of classes that he wishes to take and presses submit     SONY VGP-BPS13A/Q Battery .

In this scenario, higher priorities often take up precedence. A school registration system probably uses this technique when the server receives two registration transactions. If one student had 22 credits and the other had 100 credits, the person with 100 credits would take priority (Value based scheduling)         SONY VGP-BPS13A/Q Battery .

Timing constraints and deadlines

A system that correctly perceives the serialization and timing constraints associated with transactions with soft or firm deadlines, takes advantage of absolute consistency (Lee). Another way of making sure that data is absolute is using relative constraints  SONY VGP-BPS13B/Q Battery .

Relative constraints ensure transactions enter into the system at the same time as the rest of the group that the data transaction is associated with. Using the mechanisms of absolute and relative constraints greatly ensures the accuracy of data   SONY VGP-BPS13B/Q Battery .

An additional way of dealing with conflict resolution in a real-time database system besides deadlines is a wait policy method. This process helps ensure the latest information in time critical systems. The policy avoids conflict by asking all non-requesting blocks to wait until the most essential block of data is processed (Abbot)   SONY VGP-BPS13/Q Battery .

While studies in labs have found that data-deadline based policies do not improve performance significantly, the forced wait policy can improve performance by 50 percent (Porkka). The forced wait policy may involve waiting for higher priority transactions to process in order to prevent deadlock      SONY VGP-BPS13/Q Battery .

Another example of when data can be delayed is when a block of data is about to expire. The forced wait policy delays processing until the data is updated using new input data. The latter method helps increase the accuracy of the system and can cut down on the number of necessary processes that are aborted (Kang)       SONY VGP-BPS21A/B Battery .

Generally relying on wait policies is a not optimal (Kang).

It is necessary to discuss the formation of deadlines. Deadlines are the constraints for soon-to-be replaced data accessed by the transaction. Deadlines can be either observant or predictive (Kang)        SONY VGP-BPS21/S Battery .

In an observant deadline system, all unfinished transactions are examined and the processor determines whether any had met its deadline (Abbot). Problems arise in this method because of variations caused by seek time variations, buffer management and page faults (An Overview of Real-Time Database Systems)    SONY VGP-BPS21B Battery .

A more stable way of organizing deadlines is the predictive method. It builds a candidate schedule and determines if a transaction would miss its deadline under the schedule (Abbot).

The type of response to a missed deadline depends on whether the deadline is hard, soft, or firm       SONY VGP-BPS21A Battery .

Hard deadlines require that each data packet reach its destination before the packet has expired and if not, the process could be lost, causing a possible problem. Problems like these are not very common because omnipotence of the system is required before assigning deadlines to determine worst case      SONY VGP-BPS21 Battery .

This is very hard to do and if something unexpected happens to the system such as a minute hardware glitch, it could throw the data off. For soft or firm deadlines, missing a deadline can lead to a degraded performance but not a catastrophe (Haritsa). A soft deadline meets as many deadlines as possible      Sony VGP-BPS21A/B Battery .

However, no guarantee exists that the system can meet all deadlines. Should a transaction miss its deadline, the system has more flexibility and the transaction may increase in importance. Below is a description of these responses    Sony VGP-BPS21/S Battery :

Hard deadline: If not meeting deadlines creates problems, a hard deadline is best. It is periodic, meaning that it enters the database on a regular rhythmic pattern. An example is data gathered by a sensor. These are often used in life critical systems (Stankovic)  Sony VGP-BPS21A Battery .

Firm deadline: Firm deadlines appear to be similar to hard deadlines yet they differ from hard deadlines because firm deadlines measure how important it is to complete the transaction at some point after the transaction arrives. Sometimes completing a transaction after its deadline has expired may be harmful or not helpful, and both the firm and hard deadlines consider this  Sony VGP-BPS21 Battery .

An example of a firm deadline is an autopilot system (Snodgrass).

Soft deadline: If meeting time constrains is desirable but missing deadlines do not cause serious damage, a soft deadline may be best. It operates on an aperiodic or irregular schedule. In fact, the arrival of each time for each task is unknown  Sony Vaio PCG-5G2L Battery .

An example is an operator switchboard for a telephone(Stankovic).

Hard deadline processes abort transactions that have passed the deadline, improving the system by cleaning out clutter that needs to be processed      Sony Vaio PCG-5G3L Battery .

Processes can clear out not only the transactions with expired deadlines but also transactions with the longest deadlines, assuming that once they reach the processor they would be obsolete. This means other transactions should be of higher priority. In addition, a system can remove the least critical transactions     Sony Vaio PCG-5J1L Battery .

When I was pre-selecting classes on during a high traffic period, a field in the database can become so busy with registration requests that it was unavailable for a while and the result of my transaction was a display of the SQL query sent and a message that said that the data is currently unavailable           Sony Vaio PCG-5K2L Battery .

This error is caused by the checker, a mechanism that checks the condition of the rules, and the rule that occurred before it (Ramamritham).

The goal of scheduling periods and deadlines is to update transactions guaranteed to complete before their deadline in such a way that the workload is minimal      Sony Vaio PCG-5J2L Battery .

With large real-time databases, buffering functions can help improve performance tremendously. A buffer is part of the database that is stored in main memory to reduce transaction response time. In order to reduce disk input and output transactions, a certain number of buffers should be allocated (O'Neil)        Sony Vaio PCG-5K1L Battery .

Sometimes multiversions are stored in buffers when the data block the transaction needs is currently in use. Later, the database has the data appended to it. Different strategies allocate buffers and must balance between taking an excessive amount of memory and having everything in one buffer that it has to search for       Sony Vaio PCG-5L1L Battery .

The goal is to eliminate search time and distribute the resources between buffer frames in order to access data quickly. A buffer manager is capable of allocating more memory, if necessary, to improve response time. The buffer manager can even determine whether a transaction that it has should advance        Sony Vaio PCG-6S2L Battery .

Buffering can improve speed in real-time systems (O'Neil)

Future database systems

Traditional databases are persistent but are incapable of dealing with dynamic data that constantly changes. Therefore, another system is needed         Sony Vaio PCG-6S3L Battery .

Real-time databases may be modified to improve accuracy and efficiency and to avoid conflict, by providing deadlines and wait periods to insure temporal consistency. Real-time database systems offer a way of monitoring a physical system and representing it in data streams to a database        Sony Vaio PCG-6V1L Battery .

A data stream, like memory, fades over time. In order to guarantee that the freshest and most accurate information is recorded there are a number of ways of checking transactions to make sure they are executed in the proper order. An online auction house provides an example of a rapidly changing database         Sony Vaio PCG-6W1L Battery .

This paper discusses the example of a school registration system.

Now database systems are faster than they were in the past. In the future, we can look forward to even faster database systems. Although we have faster systems now, an effort to reduce misses and tardy times will still be beneficial  Sony Vaio PCG-6W2L Battery.

The ability to process results in a timely and predictable manner will always be more important than fast processing. Fast processing that is misapplied is not helpful for real-time database systems. Transactions that run faster still sometimes block in such a way that they have to be aborted and restarted       Sony Vaio PCG-6W3L Battery .

In fact, faster processing hurts some real-time applications because increased speed brings more complexity and more of a chance for problems caused by a variance of speed. Faster processing makes it harder to determine which deadlines have been met successfully (Lam)        Sony Vaio PCG-7111L Battery .

With future database systems running even faster than ever, there is a need to do more studies so we can continue to have efficient systems (Lam).

The amount of research studying real-time database systems will increase because of commercial applications such as web based auction houses like e-bay        Sony Vaio PCG-7112L Battery .

More developing countries are expanding their phone systems, and the number of people with cell phones in the United States as well as other places in the world continues to grow. Also likely to spur real-time research is the exponentially increasing speed of the microprocessor        Sony Vaio PCG-7113L Battery .

This enables new technologies such as web-video conferencing and instant messenger conversations in sound and high-resolution video, which are reliant on real-time database systems. Studies of temporal consistency result in new protocols and timing constraints with the goal of handling real-time transactions more effectively (Haritsa)         Sony Vaio PCG-7133L Battery .

Database theory encapsulates a broad range of topics related to the study and research of the theoretical realm of databases and database management systems.

Theoretical aspects of data management include, among other areas, the foundations of query languages  Sony Vaio PCG-7Z2L Battery ,

computational complexity and expressive power of queries, finite model theory, database design theory, dependency theory, foundations of concurrency control and database recovery, deductive databases, temporal and spatial databases, real time databases, managing uncertain data andprobabilistic databases, and Web data   Sony Vaio PCG-8Y1L Battery .

Most research work has traditionally been based on the relational model, since this model is usually considered the simplest and most foundational model of interest. Corresponding results for other data models, such as object-oriented or semi-structured models, or, more recently, graph data models and XML, are often derivable from those for the relational model  Sony Vaio PCG-8Y2L Battery .

A central focus of database theory is on understanding the complexity and power of query languages and their connection to logic. Starting from relational algebra and first-order logic (which are equivalent by Codd's theorem) and the insight that important queries such as graph reachability are not expressible in this language    Sony Vaio PCG-8Z1L Battery ,

more powerful language based on logic programming and fixpoint logic such as datalog were studied. Another focus was on the foundations of query optimization and data integration. Here most work studied conjunctive queries, which admit query optimization even under constraints using the chase algorithm     Sony Vaio PCG-8Z2L Battery .

The main research conferences in the area are the ACM Symposium on Principles of Database Systems (PODS) and the International Conference on Database Theory (ICDT)        Sony VAIO PCG-5G2L Battery .

These devices can take either the form of an integrated circuit fitted onto the motherboard itself, called a planar device in the PCI specification, or an expansion card that fits into a slot. The PCI Local Bus is common in modern PCs, where it has displaced ISA and VESA Local Bus as the standard expansion bus, and it also appears in many other computer types   (Dell Studio XPS 1640 Battery)    .

Despite the availability of faster interfaces such as PCI-X and PCI Express, conventional PCI remains a very common interface.

The PCI specification covers the physical size of the bus (including the size and spacing of the circuit board edge electrical contacts), electrical characteristics, bus timing, and protocols       (Dell Vostro 1710 Battery)        .

The specification can be purchased from the PCI Special Interest Group (PCI-SIG).

Typical PCI cards used in PCs include: network cards, sound cards, modems, extra ports such as USB or serial, TV tuner cards and disk controllers      Dell KM958 battery .

Historically video cards were typically PCI devices, but growing bandwidth requirements soon outgrew the capabilities of PCI. PCI video cards remain available for supporting extra monitors and upgrading PCs that do not have any AGP or PCI Express slots.

Many devices traditionally provided on expansion cards are now commonly integrated onto the motherboard itself, meaning that modern PCs often have no cards fitted      Dell Studio 1555 battery .

However, PCI is still used for certain specialized cards, although many tasks traditionally performed by expansion cards may now be performed equally well by USB devices.

History

Work on PCI began at Intel's Architecture Development Lab circa 1990     Sony VGP-BPS13 battery .

A team of Intel engineers (composed primarily of ADL engineers) defined the architecture and developed a proof of concept chipset and platform (Saturn) partnering with teams in the company's desktop PC systems and core logic product organizations. The original PCI architecture team included, among others, Dave Carson, Norm Rasmussen, Brad Hosler, Ed Solari, Bruce Young, Gary Solomon, Ali Oztaskin, Tom Sakoda, Rich Haslam, Jeff Rabe, and Steve Fischer      Sony VGP-BPS13/B battery .

PCI (Peripheral Component Interconnect) was immediately put to use in servers, replacing MCA and EISA as the server expansion bus of choice. In mainstream PCs, PCI was slower to replace VESA Local Bus (VLB), and did not gain significant market penetration until late 1994 in second-generation Pentium PCs     Sony VGP-BPS13/S battery .

By 1996 VLB was all but extinct, and manufacturers had adopted PCI even for 486computers. EISA continued to be used alongside PCI through 2000. Apple Computer adopted PCI for professional Power Macintosh computers (replacing NuBus) in mid-1995, and the consumerPerforma product line (replacing LC PDS) in mid-1996       Sony VGP-BPS13A/B battery .

Later revisions of PCI added new features and performance improvements, including a 66 MHz 3.3 V standard and 133 MHz PCI-X, and the adaptation of PCI signaling to other form factors. Both PCI-X 1.0b and PCI-X 2.0 are backward compatible with some PCI standards       Sony VGP-BPS13B/B battery .

The PCI-SIG introduced the serial PCI Express in 2004. At the same time they renamed PCI as Conventional PCI. Since then, motherboard manufacturers have included progressively fewer Conventional PCI slots in favor of the new standard.

Auto Configuration           Sony VGP-BPL9 battery

PCI provides separate memory and I/O port address spaces for the x86 processor family, 64 and 32 bits, respectively. Addresses in these address spaces are assigned by software. A third address space, called the PCI Configuration Space, which uses a fixed addressing scheme, allows software to determine the amount of memory and I/O address space needed by each device  Sony VGP-BPS13B/B battery .

Each device can request up to six areas of memory space or I/O port space via its configuration space registers.

In a typical system, the firmware (or operating system) queries all PCI buses at startup time (via PCI Configuration Space) to find out what devices are present and what system resources (memory space, I/O space, interrupt lines, etc.) each needs    Sony VGP-BPL15 battery .

It then allocates the resources and tells each device what its allocation is.

The PCI configuration space also contains a small amount of device type information, which helps an operating system choose device drivers for it, or at least to have a dialogue with a user about the system configuration       Dell Inspiron E1505 battery .

Devices may have an on-board ROM containing executable code for x86 or PA-RISC processors, an Open Firmware driver, or an EFI driver. These are typically necessary for devices used during system startup, before device drivers are loaded by the operating system      Dell Latitude E6400 battery .

In addition there are PCI Latency Timers that are a mechanism for PCI Bus-Mastering devices to share the PCI bus fairly. "Fair" in this case means that devices won't use such a large portion of the available PCI bus bandwidth that other devices aren't able to get needed work done. Note, this does not apply to PCI Express         HP Pavilion dv6000 Battery .

How this works is that each PCI device that can operate in bus-master mode is required to implement a timer, called the Latency Timer, that limits the time that device can hold the PCI bus. The timer starts when the device gains bus ownership, and counts down at the rate of the PCI clock        SONY VAIO VGN-FZ Battery .

When the counter reaches zero, the device is required to release the bus. If no other devices are waiting for bus ownership, it may simply grab the bus again and transfer more data.

Interrupts

Devices are required to follow a protocol so that the interrupt lines can be shared      SONY VAIO VGN-FZ18 Battery .

The PCI bus includes four interrupt lines, all of which are available to each device. However, they are not wired in parallel as are the other PCI bus lines. The positions of the interrupt lines rotate between slots, so what appears to one device as the INTA# line is INTB# to the next and INTC# to the one after that      SONY VAIO VGN-FZ21E Battery .

Single-function devices use their INTA# for interrupt signaling, so the device load is spread fairly evenly across the four available interrupt lines. This alleviates a common problem with sharing interrupts.

PCI bridges (between two PCI buses) map the four interrupt traces on each of their sides in varying ways    SONY VAIO VGN-FW21E Battery .

Some bridges use a fixed mapping, and in others it is configurable. In the general case, software cannot determine which interrupt line a device's INTA# pin is connected to across a bridge. The mapping of PCI interrupt lines onto system interrupt lines, through the PCI host bridge, is similarly implementation-dependent       SONY VAIO VGN-NR11S/S Battery .

The result is that it can be impossible to determine how a PCI device's interrupts will appear to software. Platform-specific BIOS code is meant to know this, and set a field in each device's configuration space indicating which IRQ it is connected to, but this process is not reliable      SONY VAIO VGN-NR11M/S Battery .

PCI interrupt lines are level-triggered. This was chosen over edge-triggering in order to gain an advantage when servicing a shared interrupt line, and for robustness: edge triggered interrupts are easy to miss.

Later revisions of the PCI specification add support for message-signaled interrupts        SONY VAIO VGN-NR11Z/S Battery .

In this system a device signals its need for service by performing a memory write, rather than by asserting a dedicated line. This alleviates the problem of scarcity of interrupt lines. Even if interrupt vectors are still shared, it does not suffer the sharing problems of level-triggered interrupts        SONY VAIO VGN-NR11Z/T Battery .

It also resolves the routing problem, because the memory write is not unpredictably modified between device and host. Finally, because the message signaling is in-band, it resolves some synchronization problems that can occur with posted writes and out-of-band interrupt lines       Sony VAIO VGN-FZ21E Battery .

PCI Express does not have physical interrupt lines at all. It uses message-signaled interrupts exclusively.

Conventional hardware specifications

Diagram showing the different key positions for 32-bit and 64-bit PCI cards

These specifications represent the most common version of PCI used in normal PCs    Sony VAIO VGN-FW21E Battery .

• 33.33 MHz clock with synchronous transfers
• peak transfer rate of 133 MB/s (133 megabytes per second) for 32-bit bus width (33.33 MHz × 32 bits ÷ 8 bits/byte = 133 MB/s)
• 32-bit bus width
• 32- or 64-bit memory address space (4 gigabytes or 16 exabytes)        Sony VAIO VGN-NR11S/S Battery
• 32-bit I/O port space
• 256-byte (per device) configuration space
• 5-volt signaling
• reflected-wave switching         Sony VAIO VGN-NR11Z/S Battery

The PCI specification also provides options for 3.3 V signaling, 64-bit bus width, and 66 MHz clocking, but these are not commonly encountered outside of PCI-X support on server motherboards.

The PCI bus arbiter performs bus arbitration among multiple masters on the PCI bus       Sony VAIO VGN-NR11M/S Battery .

Any number of bus masters can reside on the PCI bus, as well as requests for the bus. One pair of request and grant signals is dedicated to each bus master.

Card keying

A PCI-X Gigabit Ethernet expansion card. Note both 5 V and 3.3 V support notches are present   Sony VAIO VGN-NR11Z/T Battery .

Typical PCI cards present either one or two key notches, depending on their signaling voltage. Cards requiring 3.3 volts have a notch 56.21 mm from the front of the card (where the external connectors are) while those requiring 5 volts have a notch 104.47 mm from the front of the card         SONY VAIO VGN-FZ180E Battery .

So called "Universal cards" have both key notches and can accept both types of signal.

Connector pinout

The PCI connector is defined as having 62 contacts on each side of the edge connector, but two or four of them are replaced by key notches, so a card has 60 or 58 contacts on each side        SONY VAIO VGN-FZ220E Battery .

Pin 1 is closest to the backplate. B and A sides are as follows, looking down into the motherboard connector.

Most lines are connected to each slot in parallel. The exceptions are:

• Each slot has its own REQ# output to, and GNT# input from the motherboard arbiter.
• Each slot has its own IDSEL line, usually connected to a specific AD line   SONY VAIO VGN-FZ340E Battery .
• TDO is daisy-chained to the following slot's TDI. Cards without JTAG support must connect TDI to TDO so as not to break the chain.
• PRSNT1# and PRSNT2# for each slot have their own pull-up resistors on the motherboard. The motherboard may (but does not have to) sense these pins to determine the presence of PCI cards and their power requirements  SONY VAIO VGN-FZ430E Battery .
• REQ64# and ACK64# are individually pulled up on 32-bit only slots.
• The interrupt lines INTA# through INTD# are connected to all slots in different orders. (INTA# on one slot is INTB# on the next and INTC# on the one after that.         SONY VAIO VGN-FZ460E Battery

Notes:

• IOPWR is +3.3V or +5V, depending on the backplane. The slots also have a ridge in one of two places which prevents insertion of cards that do not have the corresponding key notch, indicating support for that voltage standard. Universal cards have both key notches and use IOPWR to determine their I/O signal levels     SONY VAIO VGN-FZ480E Battery .
• The PCI SIG strongly encourages 3.3 V PCI signaling, requiring support for it since standard revision 2.3, but most PC motherboards use the 5 V variant. Thus, while many currently available PCI cards support both, and have two key notches to indicate that, there are still a large number of 5 V-only cards on the market           SONY VAIO VGN-FZ4000 Battery .
• The M66EN pin is an additional ground on 5V PCI buses found in most PC motherboards. Cards and motherboards that do not support 66 MHz operation also ground this pin. If all participants support 66 MHz operation, a pull-up resistor on the motherboard raises this signal high and 66 MHz operation is enabled        SONY VAIO VGN-FZ31E Battery .
• At least one of PRSNT1# and PRSNT2# must be grounded by the card. The combination chosen indicates the total power requirements of the card (25 W, 15 W, or 7.5 W).
• SBO# and SDONE are signals from a cache controller to the current target. They are not initiator outputs, but are colored that way because they are target inputs      SONY VAIO VGN-FZ31B Battery .

Physical card dimensions

Full-size card

The original "full-size" PCI card is specified as a height of 107 mm (4.2 inches) and a depth of 312 mm (12.283 inches). The height includes the edge card connector       SONY VAIO VGN-FZ31J Battery .

However, most modern PCI cards are half-length or smaller (see below) and many modern PCs cannot fit a full-size card.

Card backplate

In addition to these dimensions the physical size and location of a card's backplate are also standardized     SONY VAIO VGN-FZ31M Battery .

The backplate is the part that fastens to the card cage to stabilize the card and also contains external connectors, so it usually attaches in a window so it is accessible from outside the computer case. The backplate is fixed to the cage by a 6-32 screw.

The card itself can be a smaller size, but the backplate must still be full-size and properly located so that the card fits in any standard PCI slot     SONY VAIO VGN-FZ31Z Battery .

Half-length extension card (de-facto standard)

This is in fact the practical standard now – the majority of modern PCI cards fit inside this length.

• Width: 0.6 inches (15.24 mm)
• Depth: 6.9 inches (175.26 mm)    SONY VAIO VGN-FZ38M Battery
• Height: 4.2 inches (106.68 mm)

Low-profile (half-height) card

The PCI organization has defined a standard for "low-profile" cards, which basically fit in the following ranges:

• Height: 1.42 inches (36.07 mm) to 2.536 inches (64.41 mm)
• Depth: 4.721 inches (119.91 mm) to 6.6 inches (167.64 mm)       SONY VGP-BPS8 Battery

The bracket is also reduced in height, to a standard 3.118 inches (79.2 mm). The smaller bracket will not fit a standard PC case, but will fit in a 2U rack-mount case. Many manufacturers supply both types of bracket (brackets are typically screwed to the card so changing them is not difficult)       SONY VGP-BPS13 Battery .

These cards may be known by other names such as "slim".

Mini PCI was added to PCI version 2.2 for use in laptops; it uses a 32-bit, 33 MHz bus with powered connections (3.3 V only; 5 V is limited to 100 mA) and support for bus mastering and DMA        SONY VGP-BPS13/S Battery .

The standard size for Mini PCI cards is approximately 1/4 of their full-sized counterparts. As there is limited external access to the card compared to desktop PCI cards, there are limitations on the functions they may perform.

PCI-to-MiniPCI converter Type III        SONY VGP-BPS13A/B Battery

MiniPCI and MiniPCI Express cards in comparison

Many Mini PCI devices were developed such as Wi-Fi, Fast Ethernet, Bluetooth, modems (often Winmodems), sound cards, cryptographic accelerators, SCSI, IDE–ATA, SATA controllers and combination cards       SONY VGP-BPS13B/B Battery .

Mini PCI cards can be used with regular PCI-equipped hardware, using Mini PCI-to-PCI converters. Mini PCI has been superseded by PCI Express Mini Card.

Technical details of Mini PCI       SONY VGP-BPS13A/S Battery

Mini PCI cards have a 2 W maximum power consumption, which also limits the functionality that can be implemented in this form factor. They also are required to support the CLKRUN# PCI signal used to start and stop the PCI clock for power management purposes        SONY VGP-BPS13AS Battery .

There are three card form factors: Type I, Type II, and Type III cards. The card connector used for each type include: Type I and II use a 100-pin stacking connector, while Type III uses a 124-pin edge connector, i.e. the connector for Types I and II differs from that for Type III, where the connector is on the edge of a card, like with a SO-DIMM       Dell Inspiron 1320n Battery .

The additional 24 pins provide the extra signals required to route I/O back through the system connector (audio, AC-Link, LAN, phone-line interface). Type II cards have RJ11 and RJ45 mounted connectors. These cards must be located at the edge of the computer or docking station so that the RJ11 and RJ45 ports can be mounted for external access      Dell Inspiron 1464 Battery .

Type Card on outer edge of host system          Connector        Size  Comments

IA     No    100-Pin Stacking       7.5 × 70 × 45 mm     Large Z dimension (7.5 mm)

IB     No    100-Pin Stacking       5.5 × 70 × 45 mm     Smaller Z dimension (5.5 mm)  Dell Inspiron 1564 Battery

IIA    Yes   100-Pin Stacking       17.44 × 70 × 45 mm          Large Z dimension (17.44 mm)

IIB    Yes   100-Pin Stacking       5.5 × 78 × 45 mm     Smaller Z dimension (5.5 mm)

IIIA   No    124-Pin Card Edge   2.4 × 59.6 × 50.95 mm     Larger Y dimension (50.95 mm)   Dell Inspiron 1764 Battery

IIIB   No    124-Pin Card Edge   2.4 × 59.6 × 44.6 mm       Smaller Y dimension (44.6 mm)

Mini PCI should not be confused with 144-pin Micro PCI.    Dell Studio 1450 Battery

Other physical variations

Typically consumer systems specify "N × PCI slots" without specifying actual dimensions of the space available. In some small-form-factor systems, this may not be sufficient to allow even "half-length" PCI cards to fit   Dell Studio 1457 Battery .

Despite this limitation, these systems are still useful because many modern PCI cards are considerably smaller than half-length.

PCI bus transactions

PCI bus traffic is made of a series of PCI bus transactions. Each transaction is made up of an address phase followed by one or more data phases       Dell Latitude D610 Battery .

The direction of the data phases may be from initiator to target (write transaction) or vice-versa (read transaction), but all of the data phases must be in the same direction. Either party may pause or halt the data phases at any point     Toshiba NB100 Battery .

(One common example is a low-performance PCI device that does not support burst transactions, and always halts a transaction after the first data phase.)

Any PCI device may initiate a transaction. First, it must request permission from a PCI bus arbiter on the motherboard. The arbiter grants permission to one of the requesting devices     Toshiba Satellite M65 battery .

The initiator begins the address phase by broadcasting a 32-bit address plus a 4-bit command code, then waits for a target to respond. All other devices examine this address and one of them responds a few cycles later.

64-bit addressing is done using a two-stage address phase        Toshiba Satellite M60 battery .

The initiator broadcasts the low 32 address bits, accompanied by a special "dual address cycle" command code. Devices which do not support 64-bit addressing can simply not respond to that command code. The next cycle, the initiator transmits the high 32 address bits, plus the real command code       Dell Latitude D830 Battery .

The transaction operates identically from that point on. To ensure compatibility with 32-bit PCI devices, it is forbidden to use a dual address cycle if not necessary, i.e. if the high-order address bits are all zero.

While the PCI bus transfers 32 bits per data phase, the initiator transmits a 4-bit byte mask indicating which 8-bit bytes are to be considered significant     Dell Latitude D620 Battery .

In particular, a masked write must affect only the desired bytes in the target PCI device.

PCI address spaces

PCI has three address spaces: memory, I/O address, and configuration       Dell Inspiron Mini 10 Battery .

Memory addresses are 32 bits (optionally 64 bits) in size, support caching and can be burst transactions.

I/O addresses are for compatibility with the Intel x86 architecture's I/O port address space. Although the PCI bus specification allows burst transactions in any address space, most devices only support it for memory addresses and not I/O  Sony VGN-FW11S Battery .

Finally, PCI configuration space provides access to 256 bytes of special configuration registers per PCI device. Each PCI slot gets its own configuration space address range. The registers are used to configure devices memory and I/O address ranges they should respond to from transaction initiators       Sony VGN-FW11M Battery .

When a computer is first turned on, all PCI devices respond only to their configuration space accesses. The computers BIOS scans for devices and assigns Memory and I/O address ranges to them.

If an address is not claimed by any device, the transaction initiator's address phase will time out causing the initiator to abort the operation       Sony VGN-FW139E/H battery .

In case of reads, it is customary to supply all-ones for the read data value (0xFFFFFFFF) in this case. PCI devices therefore generally attempt to avoid using the all-ones value in important status registers, so that such an error can be easily detected by software    Dell Latitude E5400 Battery .

PCI command codes

There are 16 possible 4-bit command codes, and 12 of them are assigned. With the exception of the unique dual address cycle, the least significant bit of the command code indicates whether the following data phases are a read (data sent from target to initiator) or a write (data sent from an initiator to target)     Dell Latitude E4200 Battery .

PCI targets must examine the command code as well as the address and not respond to address phases which specify an unsupported command code.

The commands that refer to cache lines depend on the PCI configuration space cache line size register being set up properly; they may not be used until that has been done    Dell Inspiron 300M Battery .

0000: Interrupt Acknowledge

This is a special form of read cycle implicitly addressed to the interrupt controller, which returns an interrupt vector. The 32-bit address field is ignored      Dell Vostro A840 Battery .

One possible implementation is to generate an interrupt acknowledge cycle on an ISA bus using a PCI/ISA bus bridge. This command is for IBM PC compatibility; if there is no Intel 8259 style interrupt controller on the PCI bus, this cycle need never be used  Dell Studio 1737 battery .

0001: Special Cycle

This cycle is a special broadcast write of system events that PCI card may be interested in. The address field of a special cycle is ignored, but it is followed by a data phase containing a payload message       Dell Inspiron E1505 battery .

The currently defined messages announce that the processor is stopping for some reason (e.g. to save power). No device ever responds to this cycle; it is always terminated with a master abort after leaving the data on the bus for at least 4 cycles   Dell RM791 battery .

0010: I/O Read

This performs a read from I/O space. All 32 bits of the read address are provided, so that a device can (for compatibility reasons) implement less than 4 bytes worth of I/O registers         Dell XPS M1530 battery .

If the byte enables request data not within the address range supported by the PCI device (e.g. a 4-byte read from a device which only supports 2 bytes of I/O address space), it must be terminated with a target abort. Multiple data cycles are permitted, using linear (simple incrementing) burst ordering        Dell XPS M2010 battery .

The PCI standard is discouraging the use of I/O space in new devices, preferring that as much as possible be done through main memory mapping.

0011: I/O Write

This performs a write to I/O space.

010x: Reserved

A PCI device must not respond to an address cycle with these command codes         Acer Aspire One battery .

0110: Memory Read

This performs a read cycle from memory space. Because the smallest memory space a PCI device is permitted to implement is 16 bits, the two least significant bits of the address are not needed; equivalent information will arrive in the form of byte select signals  Toshiba Satellite P10 Battery .

They instead specify the order in which burst data must be returned. If a device does not support the requested order, it must provide the first word and then disconnect.

If a memory space is marked as "prefetchable", then the target device must ignore the byte select signals on a memory read and always return 32 valid bits       SONY VGN-FZ210CE Battery .

0111: Memory Write

This operates similarly to a memory read. The byte select signals are more important in a write, as unselected bytes must not be written to memory.

Generally, PCI writes are faster than PCI reads, because a device can buffer the incoming write data and release the bus faster   Dell Precision M70 Battery .

For a read, it must delay the data phase until the data has been fetched.

100x: Reserved

A PCI device must not respond to an address cycle with these command codes  Toshiba Satellite L305 Battery .

1010: Configuration Read

This is similar to an I/O read, but reads from PCI configuration space. A device must respond only if the low 11 bits of the address specify a function and register that it implements, and if the special IDSEL signal is asserted. It must ignore the high 21 bits. Burst reads (using linear incrementing) are permitted in PCI configuration space       Toshiba Satellite T4900 Battery .

Unlike I/O space, standard PCI configuration registers are defined so that reads never disturb the state of the device. It is possible for a device to have configuration space registers beyond the standard 64 bytes which have read side effects, but this is rare     Toshiba PA3399U-2BRS battery .

Configuration space accesses often have a few cycles of delay in order to allow the IDSEL lines to stabilize, which makes them slower than other forms of access. Also, a configuration space access requires a multi-step operation rather than a single machine instruction. Thus, it is best to avoid them during routine operation of a PCI device         Toshiba Satellite A200 Battery .

1011: Configuration Write

This operates analogously to a configuration read.

1100: Memory Read Multiple        Toshiba Satellite 1200 Battery

This command is identical to a generic memory read, but includes the hint that a long read burst will continue beyond the end of the current cache line, and the target should internally prefetch a large amount of data . A target is always permitted to consider this a synonym for a generic memory read       Toshiba Satellite M300 Battery .

1101: Dual Address Cycle

When accessing a memory address that requires more than 32 bits to represent, the address phase begins with this command and the low 32 bits of the address, followed by a second cycle with the actual command and the high 32 bits of the address   SONY VGP-BPS13A/Q Battery .

PCI targets that do not support 64-bit addressing can simply treat this as another reserved command code and not respond to it. This command code can only be used with a non-zero high-order address word; it is forbidden to use this cycle if not necessary      SONY VGP-BPS13A/Q Battery .

1110: Memory Read Line

This command is identical to a generic memory read, but includes the hint that the read will continue to the end of the cache line. A target is always permitted to consider this a synonym for a generic memory read         SONY VGP-BPS13B/Q Battery .

1111: Memory Write and Invalidate

This command is identical to a generic memory write, but comes with the guarantee that one or more whole cache lines will be written, with all byte selects enabled. This is an optimization for write-back caches snooping the bus        SONY VGP-BPS13B/Q Battery.

Normally, a write-back cache holding dirty data must interrupt the write operation long enough write its own dirty data first. If the write is performed using this command, the data to be written back is guaranteed to be irrelevant, and can simply be invalidated in the write-back cache       SONY VGP-BPS13/Q Battery .

This optimization only affects the snooping cache, and makes no difference to the target, which may treat this as a synonym for the memory write command.

PCI bus signals

PCI bus transactions are controlled by five main control signals, two driven by the initiator of a transaction (FRAME# and IRDY#), and three driven by the target (DEVSEL#, TRDY#, and STOP#)       SONY VGP-BPS13/Q Battery .

There are two additional arbitration signals (REQ# and GNT#) which are used to obtain permission to initiate a transaction. All are active-low, meaning that the active or asserted state is a low voltage. Pull-up resistors on the motherboard ensure they will remain high (inactive or deasserted) if not driven by any device         SONY VGP-BPS21A/B Battery ,

but the PCI bus does not depend on the resistors to change the signal level; all devices drive the signals high for one cycle before ceasing to drive the signals.

Signal timing

All PCI bus signals are sampled on the rising edge of the clock       SONY VGP-BPS21/S Battery .

Signals nominally change on the falling edge of the clock, giving each PCI device approximately one half a clock cycle to decide how to respond to the signals it observed on the rising edge, and one half a clock cycle to transmit its response to the other device.

The PCI bus requires that every time the device driving a PCI bus signal changes, one turnaround cycle must elapse between the time the one device stops driving the signal and the other device starts        SONY VGP-BPS21B Battery .

Without this, there might be a period when both devices were driving the signal, which would interfere with bus operation.

The combination of this turnaround cycle and the requirement to drive a control line high for one cycle before ceasing to drive it means that each of the main control lines must be high for a minimum of two cycles when changing owners    SONY VGP-BPS21A Battery .

The PCI bus protocol is designed so this is rarely a limitation; only in a few special cases (notably fast back-to-back transactions) is it necessary to insert additional delay to meet this requirement.

Arbitration

Any device on a PCI bus that is capable of acting as a bus master may initiate a transaction with any other device   SONY VGP-BPS21 Battery .

To ensure that only one transaction is initiated at a time, each master must first wait for a bus grant signal, GNT#, from an arbiter located on the motherboard. Each device has a separate request line REQ# that requests the bus, but the arbiter may "park" the bus grant signal at any device if there are no current requests       Sony VGP-BPS21A/B Battery .

The arbiter may remove GNT# at any time. A device which loses GNT# may complete its current transaction, but may not start one (by asserting FRAME#) unless it observes GNT# asserted the cycle before it begins        Sony VGP-BPS21/S Battery .

The arbiter may also provide GNT# at any time, including during another master's transaction. During a transaction, either FRAME# or IRDY# or both are asserted; when both are deasserted, the bus is idle. A device may initiate a transaction at any time that GNT# is asserted and the bus is idle       Sony VGP-BPS21A Battery .

Address phase

A PCI bus transaction begins with an address phase. The initiator, seeing that it has GNT# and the bus is idle, drives the target address onto the AD[31:0] lines, the associated command (e.g. memory read, or I/O write) on the C/BE[3:0]# lines, and pulls FRAME# low  Sony VGP-BPS21 Battery .

Each other device examines the address and command and decides whether to respond as the target by asserting DEVSEL#. A device must respond by asserting DEVSEL# within 3 cycles. Devices which promise to respond within 1 or 2 cycles are said to have "fast DEVSEL" or "medium DEVSEL", respectively        Sony Vaio PCG-5G2L Battery .

(Actually, the time to respond is 2.5 cycles, since PCI devices must transmit all signals half a cycle early so that they can be received three cycles later.)

Note that a device must latch the address on the first cycle; the initiator is required to remove the address and command from the bus on the following cycle, even before receiving a DEVSEL# response    Sony Vaio PCG-5G3L Battery .

The additional time is available only for interpreting the address and command after it is captured.

On the fifth cycle of the address phase (or earlier if all other devices have medium DEVSEL or faster), a catch-all "subtractive decoding" is allowed for some address ranges       Sony Vaio PCG-5J1L Battery .

This is commonly used by an ISA bus bridge for addresses within its range (24 bits for memory and 16 bits for I/O).

On the sixth cycle, if there has been no response, the initiator may abort the transaction by deasserting FRAME#. This is known as master abort termination and it is customary for PCI bus bridges to return all-ones data (0xFFFFFFFF) in this case   Sony Vaio PCG-5K2L Battery .

PCI devices therefore are generally designed to avoid using the all-ones value in important status registers, so that such an error can be easily detected by software.

Address phase timing

On the rising edge of clock 0, the initiator observes FRAME# and IRDY# both high, and GNT# low, so it drives the address, command, and asserts FRAME# in time for the rising edge of clock 1         Sony Vaio PCG-5J2L Battery .

Targets latch the address and begin decoding it. They may respond with DEVSEL# in time for clock 2 (fast DEVSEL), 3 (medium) or 4 (slow). Subtractive decode devices, seeing no other response by clock 4, may respond on clock 5. If the master does not see a response by clock 5, it will terminate the transaction and remove FRAME# on clock 6      Sony Vaio PCG-5K1L Battery .

TRDY# and STOP# are deasserted (high) during the address phase. The initiator may assert IRDY# as soon as it is ready to transfer data, which could theoretically be as soon as clock 2.

Dual-cycle address

To allow 64-bit addressing, a master will present the address over two consecutive cycles      Sony Vaio PCG-5L1L Battery .

First, it sends the low-order address bits with a special "dual-cycle address" command on the C/BE[3:0]#. On the following cycle, it sends the high-order address bits and the actual command. Dual-address cycles are forbidden if the high-order address bits are zero, so devices which do not support 64-bit addressing can simply not respond to dual cycle commands     Sony Vaio PCG-6S2L Battery .

Configuration access

Addresses for PCI configuration space access are decoded specially. For these, the low-order address lines specify the offset of the desired PCI configuration register, and the high-order address lines are ignored. Instead, an additional address signal, the IDSEL input, must be high before a device may assert DEVSEL#        Sony Vaio PCG-6S3L Battery .

Each slot connects a different high-order address line to the IDSEL pin, and is selected using one-hot encoding on the upper address lines.

Data phases

After the address phase (specifically, beginning with the cycle that DEVSEL# goes low) comes a burst of one or more data phases  Sony Vaio PCG-6V1L Battery .

In all cases, the initiator drives active-low byte select signals on the C/BE[3:0]# lines, but the data on the AD[31:0] may be driven by the initiator (in case of writes) or target (in case of reads).

During data phases, the C/BE[3:0]# lines are interpreted as active-low byte enables        Sony Vaio PCG-6W1L Battery .

In case of a write, the asserted signals indicate which of the four bytes on the AD bus are to be written to the addressed location. In the case of a read, they indicate which bytes the initiator is interested in. For reads, it is always legal to ignore the byte enable signals and simply return all 32 bits      Sony Vaio PCG-6W2L Battery ;

cacheable memory resources are required to always return 32 valid bits. The byte enables are mainly useful for I/O space accesses where reads have side effects.

A data phase with all four C/BE# lines deasserted is explicitly permitted by the PCI standard, and must have no effect on the target (other than to advance the address in the burst access in progress)       Sony Vaio PCG-6W3L Battery .

The data phase continues until both parties are ready to complete the transfer and continue to the next data phase. The initiator asserts IRDY# (initiator ready) when it no longer needs to wait, while the target asserts TRDY# (target ready). Whichever side is providing the data must drive it on the AD bus before asserting its ready signal         Sony Vaio PCG-7111L Battery .

Once one of the participants asserts its ready signal, it may not become un-ready or otherwise alter its control signals until the end of the data phase. The data recipient must latch the AD bus each cycle until it sees both IRDY# and TRDY# asserted, which marks the end of the current data phase and indicates that the just-latched data is the word to be transferred  Sony Vaio PCG-7112L Battery .

To maintain full burst speed, the data sender then has half a clock cycle after seeing both IRDY# and TRDY# asserted to drive the next word onto the AD bus.

This continues the address cycle illustrated above, assuming a single address cycle with medium DEVSEL, so the target responds in time for clock 3         Sony Vaio PCG-7113L Battery .

However, at that time, neither side is ready to transfer data. For clock 4, the initiator is ready, but the target is not. On clock 5, both are ready, and a data transfer takes place (as indicated by the vertical lines). For clock 6, the target is ready to transfer, but the initator is not      Sony Vaio PCG-7133L Battery .

On clock 7, the initiator becomes ready, and data is transferred. For clocks 8 and 9, both sides remain ready to transfer data, and data is transferred at the maximum possible rate (32 bits per clock cycle)          Sony Vaio PCG-7Z2L Battery .

In case of a read, clock 2 is reserved for turning around the AD bus, so the target is not permitted to drive data on the bus even if it is capable of fast DEVSEL.

Fast DEVSEL# on reads

A target that supports fast DEVSEL could in theory begin responding to a read the cycle after the address is presented  Sony Vaio PCG-8Y1L Battery .

This cycle is, however, reserved for AD bus turnaround. Thus, a target may not drive the AD bus (and thus may not assert TRDY#) on the second cycle of a transaction. Note that most targets will not be this fast and will not need any special logic to enforce this condition         Sony Vaio PCG-8Y2L Battery .

Ending transactions

Either side may request that a burst end after the current data phase. Simple PCI devices that do not support multi-word bursts will always request this immediately. Even devices that do support bursts will have some limit on the maximum length they can support, such as the end of their addressable memory         Sony Vaio PCG-8Z1L Battery .

Initiator burst termination

The initiator can mark any data phase as the final one in a transaction by deasserting FRAME# at the same time as it asserts IRDY#. The cycle after the target asserts TRDY#, the final data transfer is complete, both sides deassert their respective RDY# signals, and the bus is idle again         Sony Vaio PCG-8Z2L Battery .

The master may not deassert FRAME# before asserting IRDY#, nor may it deassert FRAME# while waiting, with IRDY# asserted, for the target to assert TRDY#.

The only minor exception is a master abort termination, when no target responds with DEVSEL#        Sony VAIO PCG-5G2L Battery .

Obviously, it is pointless to wait for TRDY# in such a case. However, even in this case, the master must assert IRDY# for at least one cycle after deasserting FRAME#. (Commonly, a master will assert IRDY# before receiving DEVSEL#, so it must simply hold IRDY# asserted for one cycle longer.)        Sony VAIO PCG-5G3L Battery

This is to ensure that bus turnaround timing rules are obeyed on the FRAME# line.

Target burst termination

The target requests the initiator end a burst by asserting STOP#. The initiator will then end the transaction by deasserting FRAME# at the next legal opportunity; if it wishes to transfer more data, it will continue in a separate transaction       Sony VAIO PCG-5J1L Battery .

There are several ways for the target to do this:

Disconnect with data

If the target asserts STOP# and TRDY# at the same time, this indicates that the target wishes this to be the last data phase  Sony VAIO PCG-5K2L Battery .

For example, a target that does not support burst transfers will always do this to force single-word PCI transactions. This is the most efficient way for a target to end a burst.

Disconnect without data

If the target asserts STOP# without asserting TRDY#, this indicates that the target wishes to stop without transferring data   Sony VAIO PCG-5J2L Battery .

STOP# is considered equivalent to TRDY# for the purpose of ending a data phase, but no data is transferred.

Retry

A Disconnect without data before transferring any data is a retry, and unlike other PCI transactions, PCI initiators are required to pause slightly before continuing the operation. See the PCI specification for details       Sony VAIO PCG-5K1L Battery .

Target abort

Normally, a target holds DEVSEL# asserted through the last data phase. However, if a target deasserts DEVSEL# before disconnecting without data (asserting STOP#), this indicates a target abort, which is a fatal error condition. The initiator may not retry, and typically treats it as a bus error      Sony VAIO PCG-5L1L Battery .

Note that a target may not deassert DEVSEL# while waiting with TRDY# or STOP# low; it must do this at the beginning of a data phase.

There will always be at least one more cycle after a target-initiated disconnection, to allow the master to deassert FRAME#   Sony VAIO PCG-6S2L Battery .

There are two sub-cases, which take the same amount of time, but one requires an additional data phase:

Disconnect-A

If the initiator observes STOP# before asserting its own IRDY#, then it can end the burst by deasserting FRAME# at the end of the current data phase       Sony VAIO PCG-6S3L Battery .

Disconnect-B

If the initiator has already asserted IRDY# (without deasserting FRAME#) by the time it observes the target's STOP#, it is already committed to an additional data phase. The target must wait through an additional data phase, holding STOP# asserted without TRDY#, before the transaction can end        Sony VAIO PCG-6V1L Battery .

If the initiator ends the burst at the same time as the target requests disconnection, there is no additional bus cycle.

Burst addressing

For memory space accesses, the words in a burst may be accessed in several orders. The unnecessary low-order address bits AD[1:0] are used to convey the initiator's requested order        Sony VAIO PCG-6W1L Battery .

A target which does not support a particular order must terminate the burst after the first word. Some of these orders depend on the cache line size, which is configurable on all PCI devices.

PCI burst ordering

A[1]  A[0]  Burst order (with 16-byte cache line)

0       0       Linear incrementing (0x0C, 0x10, 0x14, 0x18, 0x1C, ...)         Sony VAIO PCG-6W2L Battery

0       1       Cacheline toggle (0x0C, 0x08, 0x04, 0x00, 0x1C, 0x18, ...)

1       0       Cacheline wrap (0x0C, 0x00, 0x04, 0x08, 0x1C, 0x10, ...)

1       1       Reserved (disconnect after first transfer)         Sony VAIO PCG-6W3L Battery

If the starting offset within the cache line is zero, all of these modes reduce to the same order.

Cache line toggle and cache line wrap modes are two forms of critical-word-first cache line fetching. Toggle mode XORs the supplied address with an incrementing counter. This is the native order for Intel 486 and Pentium processors     Sony VAIO PCG-7111L Battery.

It has the advantage that it is not necessary to know the cache line size to implement it.

PCI version 2.1 obsoleted toggle mode and added the cache line wrap mode,  where fetching proceeds linearly, wrapping around at the end of each cache line      Sony VAIO PCG-7112L Battery .

When one cache line is completely fetched, fetching jumps to the starting offset in the next cache line.

Note that most PCI devices only support a limited range of typical cache line sizes; if the cache line size is programmed to an unexpected value, they force single-word access         Sony VAIO PCG-7113L Battery .

PCI also supports burst access to I/O and configuration space, but only linear mode is supported. (This is rarely used, and may be buggy in some devices; they may not support it, but not properly force single-word access either.)     Sony VAIO PCG-7Z1L Battery

Transaction examples

This is the highest-possible speed four-word write burst, terminated by the master:

On clock edge 1, the initiator starts a transaction by driving an address, command, and asserting FRAME# The other signals are idle (indicated by ^^^), pulled high by the motherboard's pull-up resistors       Sony VAIO PCG-7Z2L Battery .

That might be their turnaround cycle. On cycle 2, the target asserts both DEVSEL# and TRDY#. As the initiator is also ready, a data transfer occurs. This repeats for three more cycles, but before the last one (clock edge 5), the master deasserts FRAME#, indicating that this is the end        Sony VAIO PCG-8Y1L Battery .

On clock edge 6, the AD bus and FRAME# are undriven (turnaround cycle) and the other control lines are driven high for 1 cycle. On clock edge 7, another initiator can start a different transaction. This is also the turnaround cycle for the other control lines.

The equivalent read burst takes one more cycle, because the target must wait 1 cycle for the AD bus to turn around before it may assert TRDY#        Sony VAIO PCG-8Y2L Battery :

A high-speed burst terminated by the target will have an extra cycle at the end:

On clock edge 6, the target indicates that it wants to stop (with data), but the initiator is already holding IRDY# low, so there is a fifth data phase (clock edge 7), during which no data is transferred     WD passport essential (500GB/640GB) .

Parity

The PCI bus detects parity errors, but does not attempt to correct them by retrying operations; it is purely a failure indication. Because of this, there is no need to detect the parity error before it has happened, and the PCI bus actually detects it a few cycles later    WD passport essential (250GB/320GB) .

During a data phase, whichever device is driving the AD[31:0] lines computes even parity over them and the C/BE[3:0]# lines, and sends that out the PAR line one cycle later. All access rules and turnaround cycles for the AD bus apply to the PAR line, just one cycle later       WD  passport essential SE (750GB/1TB)       .

The device listening on the AD bus checks the received parity and asserts the PERR# (parity error) line one cycle after that. This generally generates a processor interrupt, and the processor can search the PCI bus for the device which detected the error.

The PERR# line is only used during data phases, once a target has been selected   WD  passport elite(250GB/320GB) .

If a parity error is detected during an address phase (or the data phase of a Special Cycle), the devices which observe it assert the SERR# (System error) line.

Even when some bytes are masked by the C/BE# lines and not in use, they must still have some defined value, and this value must be used to compute the parity     WD passport elite(500GB/640GB) .

Fast back-to-back transactions

Due to the need for a turnaround cycle between different devices driving PCI bus signals, in general it is necessary to have an idle cycle between PCI bus transactions. However, in some circumstances it is permitted to skip this idle cycle, going directly from the final cycle of one transfer    WD  passport studio for Mac(320GB/500GB) .

An initiator may only perform back-to-back transactions when:

they are by the same initiator (or there would be no time to turn around the C/BE# and FRAME# lines),the first transaction was a write (so there is no need to turn around the AD bus), and  the initiator still has permission (from its GNT# input) to use the PCI bus      WD  passport studio for Mac(500GB/640GB) .

Additional timing constraints may come from the need to turn around are the target control lines, particularly DEVSEL#. The target deasserts DEVSEL#, driving it high, in the cycle following the final data phase, which in the case of back-to-back transactions is the first cycle of the address phase     WD  Elements series(250GB/320GB) .

The second cycle of the address phase is then reserved for DEVSEL# turnaround, so if the target is different from the previous one, it must not assert DEVSEL# until the third cycle (medium DEVSEL speed).

One case where this problem cannot arise is if the initiator knows somehow (presumably because the addresses share sufficient high-order bits) that the second transfer is addressed to the same target as the previous one    WD  Elements SE(500GB/640GB) .

In that case, it may perform back-to-back transactions. All PCI targets must support this.

It is also possible for the target keeps track of the requirements. If it never does fast DEVSEL, they are met trivially. If it does, it must wait until medium DEVSEL time unless             WD Elements SE(750GB/1TB) :

the current transaction was preceded by an idle cycle (is not back-to-back), or

the previous transaction was to the same target, or

the current transaction began with a double address cycle          WD  Elements desktop(500GB/640GB) .

Targets which have this capability indicate it by a special bit in a PCI configuration register, and if all targets on a bus have it, all initiators may use back-to-back transfers freely.

A subtractive decoding bus bridge must know to expect this extra delay in the event of back-to-back cycles in order to advertise back-to-back support          WD  Elements desktop(750GB/1TB) .

64-bit PCI

This section explains only basic 64-bit PCI; the full PCI-X protocol extension is much more extensive.

The PCI specification includes optional 64-bit support. This is provided via an extended connector which provides the 64-bit bus extensions AD[63:32], C/BE[7:4]#, and PAR64   WD  Elements desktop(1.5 TB/2TB) .

Memory transactions between 64-bit devices may use all 64 bits to double the data transfer rate. Non-memory transactions (including configuration and I/O space accesses) may not use the 64-bit extension. During a 64-bit burst, burst addressing works just as in a 32-bit transfer, but the address is incremented twice per data phase       WD  passport essential SE (750GB/1TB)--USB 3.0)     .

The starting address must be 64-bit aligned; i.e. AD2 must be 0. The data corresponding to the intervening addresses (with AD2 = 1) is carried on the upper half of the AD bus.

To initiate a 64-bit transaction, the initiator drives the starting address on the AD bus and asserts REQ64# at the same time as FRAME#        WD  passport essential (500GB/640GB) .

If the selected target can support a 64-bit transfer for this transaction, it replies by asserting ACK64# at the same time as DEVSEL#. Note that a target may decide on a per-transaction basis whether to allow a 64-bit transfer.

If REQ64# is asserted during the address phase, the initiator also drives the high 32 bits of the address and a copy of the bus command on the high half of the bus         WD  passport for Mac(320GB/500GB) .

If the address requires 64 bits, a dual address cycle is still required, but the high half of the bus carries the upper half of the address and the final command code during both address phase cycles; this allows a 64-bit target to see the entire address and begin responding earlier        WD  passport for Mac(640GB/1TB) .

If the initiator sees DEVSEL# asserted without ACK64#, it performs 32-bit data phases. The data which would have been transferred on the upper half of the bus during the first data phase is instead transferred during the second data phase. Typically, the initiator drives all 64 bits of data before seeing DEVSEL#       My book essential 4 generation  (640GB/1TB) .

If ACK64# is missing, it may cease driving the upper half of the data bus.

The REQ64# and ACK64# lines are held asserted for the entire transaction save the last data phase, and deasserted at the same time as FRAME# and DEVSEL#, respectively       WD  My book essential 4 generation( 1.5TB/2TB) .

The PAR64 line operates just like the PAR line, but provides even parity over AD[63:32] and C/BE[7:4]#. It is only valid for address phases if REQ64# is asserted. PAR64 is only valid for data phases if both REQ64# and ACK64# are asserted.

Cache snooping (obsolete)

PCI originally included optional support for write-back cache coherence         WD  My book elite( 1TB/1.5TB) .

This required support by cacheable memory targets, which would listen to two pins from the cache on the bus, SDONE (snoop done) and SBO# (snoop backoff).

Because this was rarely implemented in practice, it was deleted from revision 2.2 of the PCI specification, and the pins re-used for SMBus access in revision 2.3        WD  My book studio(1TB/2TB) .

The cache would watch all memory accesses, without asserting DEVSEL#. If it noticed an access that might be cached, it would drive SDONE low (snoop not done). A coherence-supporting target would avoid completing a data phase (asserting TRDY#) until it observed SDONE high        WD  My book essential 4 generation( 1.5TB/2TB) .

In the case of a write to data that was clean in the cache, the cache would only have to invalidate its copy, and would assert SDONE as soon as this was established. However, if the cache contained dirty data, the cache would have to write it back before the access could proceed        WD  My book elite(640GB/2TB) .

One edge of the expansion card holds the contacts (the edge connector) that fit exactly into the slot. They establish the electrical contact between the electronics (mostly integrated circuits) on the card and on the motherboard.

Connectors mounted on the bracket allow the connection of external devices to the card     (Dell Studio XPS 1640 Battery)  .

Depending on the form factor of the motherboard and case, around one to seven expansion cards can be added to a computer system. In the case of a backplane system, up to 19 expansion cards can be installed. There are also other factors involved in expansion card capacity       (Dell Vostro 1710 Battery)       .

For example, most graphics cards on the market as of 2010 are dual slot graphics cards, using the second slot as a place to put an active heat sink with a fan.

Some cards are "low-profile" cards, meaning that they are shorter than standard cards and will fit in a lower height computer chassis  Dell KM958 battery .

(There is a "low profile PCI card" standard that specifies a much smaller bracket and board area). The group of expansion cards that are used for external connectivity, such as anetwork, SAN or modem card, are commonly referred to as input/output cards(or I/O cards)      Dell Studio 1555 battery .

The primary purpose of an expansion card is to provide or expand on features not offered by the motherboard. For example, the original IBM PC did not provide graphics or hard drive capability as the technology for providing that on the motherboard did not exist        Sony VGP-BPS13 battery .

In that case, a graphics expansion card and anST-506 hard disk controller card provided graphics capability and hard drive interface respectively.

In the case of expansion of on-board capability, a motherboard may provide a single serial RS232 port or Ethernet port         Sony VGP-BPS13/B battery .

An expansion card can be installed to offer multiple RS232 ports or multiple and higher bandwidth Ethernet ports. In this case, the motherboard provides basic functionality but the expansion card offers additional or enhanced ports      Sony VGP-BPS13/S battery .

History

The first microcomputer to feature a slot-type expansion card bus was the Altair 8800, developed 1974-1975. Initially, implementations of this bus were proprietary (such as the Apple II and Macintosh), but by 1982 manufacturers of Intel 8080/Zilog Z80-based computers running CP/M had settled around the S-100 standard          Sony VGP-BPS13A/B battery .

IBM introduced the XT bus, with the first IBM PC in 1981; it was then called the PC bus, as the IBM XT, using the same bus (with slight exception,) was not to be introduced until 1983. XT (a.k.a. 8-bit ISA) was replaced with ISA (a.k.a. 16-bit ISA), originally known as AT bus, in 1984        Sony VGP-BPS13B/B battery .

IBM's MCA bus, developed for the PS/2 in 1987, was a competitor to ISA, also their design, but fell out of favor due to the ISA's industry-wide acceptance and IBM's closed licensing of MCA. EISA, the 32-bit extended version of ISA championed by Compaq, was used on some PC motherboards until 1997, when Microsoft declared it a "legacy" subsystem in the PC 97 industry white-paper  Sony VGP-BPL9 battery .

Proprietary local buses (q.v. Compaq) and then the VESA Local Bus Standard, were late 1980s expansion buses that were tied but not exclusive to the 80386 and 80486 CPU bus. The PC104bus is an embedded bus that copies the ISA bus.

Intel launched their PCI bus chipsets along with the P5-based Pentium CPUs in 1993         Sony VGP-BPS13B/B battery .

The PCI bus was introduced in 1991 as replacement for ISA. The standard (now at version 3.0) is found on PC motherboards to this day. The PCI standard supports Bridging, as many as ten daisy chained PCI buses have been tested. Cardbus, using the PCMCIA connector, is a PCI format that attaches peripherals to the Host PCI Bus via PCI to PCI Bridge     Sony VGP-BPL15 battery .

Cardbus is being supplanted by ExpressCard format. Intel introduced the AGP bus in 1997 as a dedicated video acceleration solution. AGP devices are logically attached to the PCI bus over a PCI-to-PCI bridge. Though termed a bus, AGP usually supports only a single card at a time (Legacy BIOS support issues)      Dell Inspiron E1505 battery .

From 2005 PCI-Express has been replacing both PCI and AGP. This standard, approved in 2004, implements the logical PCI protocol over a serial communication interface. PC104-Plus, Mini PCI, or PCI-104 are often added for expansion on small form factor boards such as Micro ITX      Dell Latitude E6400 battery .

The USB format has become a de facto expansion bus standard especially for laptop computers. All the functions of add-in card slots can currently be duplicated by USB, including Video , networking, storage and audio. USB 2.0 is currently part of the ExpressCard interface and USB 3.0 is part of the ExpressCard 2.0 standard   HP Pavilion dv6000 Battery .

FireWire or IEEE 1394 is a serial expansion bus originally promoted for Apple Inc. Computer expansion replacing the SCSI bus. Also adopted for PCs, often used for storage and video cameras, it has application for networking, video, and audio.

After the S-100 bus, this article above mentions only buses used on IBM-compatible/Windows-Intel PCs   SONY VAIO VGN-FZ Battery .

Most other computer lines that were not IBM compatible, including those from Apple Inc.(Apple II, Macintosh), Tandy, Commodore, Amiga, and Atari, offered their own expansion buses. Apple used a proprietary system with seven 50-pin-slots for Apple II peripheral cards         SONY VAIO VGN-FZ18 Battery ,

then later used theNuBus for its Macintosh series until 1995, at which time they switched to a standard PCI Bus. Generally PCI expansion cards will function on any CPU platform if there is a software driver for that type. PCI video cards and other cards that contain a BIOS are problematic, although video cards conforming to VESA Standards may be used for secondary monitors  SONY VAIO VGN-FZ21E Battery .

DEC Alpha, IBM PowerPC, and NEC MIPS workstations used PCI bus connectors .

Even many video game consoles, such as the Sega Genesis, included expansion buses; at least in the case of the Genesis, the expansion bus was proprietary          SONY VAIO VGN-FW21E Battery ,

and in fact the cartridge slots of many cartridge based consoles (not including the Atari 2600) would qualify as expansion buses, as they exposed both read and write capabilities of the system's internal bus. However, the expansion modules attached to these interfaces        SONY VAIO VGN-NR11S/S Battery ,

though functionally the same as expansion cards, are not technically expansion cards, due to their physical form.

For their 1000 EX and 1000 HX models, Tandy Computer designed the PLUS expansion interface, an adaptation of the XT-bus supporting cards of a smaller form factor      SONY VAIO VGN-NR11M/S Battery .

Because it is electrically compatible with the XT bus (a.k.a. 8-bit ISA or XT-ISA), a passive adapter can be made to connect XT cards to a PLUS expansion connector. Another feature of PLUS cards is that they are stackable. Another bus that offered stackable expansion modules was the "sidecar" bus used by the IBM PCjr       SONY VAIO VGN-NR11Z/S Battery .

This may have been electrically the same as or similar to the XT bus; it most certainly had some similarities since both essentially exposed the 8088 CPU's address and data buses, with some buffering and latching, the addition of interrupts and DMA provided by Intel add-on chips, and a few system fault detection lines (Power Good, Memory Check, I/O Channel Check)  SONY VAIO VGN-NR11Z/T Battery .

Again, PCjr sidecars are not technically expansion cards, but expansion modules, with the only difference being that the sidecar is an expansion card enclosed in a plastic box (with holes exposing the connectors)        Sony VAIO VGN-FZ21E Battery .

ExpressCard is an interface to allow peripheral devices to be connected to a computer, usually a laptop computer. Formerly called NEWCARD, the ExpressCard standard specifies the design of slots built into the computer and of cards which can be inserted into ExpressCard slots      Sony VAIO VGN-FW21E Battery .

The cards containelectronic circuitry and connectors to which external devices can be connected. The ExpressCard standard replaces the PC Card (also known as PCMCIA or CardBus) standards.

ExpressCard plug-in hardware available includes connect cards, FireWire 800 (1394B), USB 3.0, 1Gb/sec Ethernet Sony VAIO VGN-NR11S/S Battery ,

Serial ATA external disk drives, solid-state drives, external enclosures for desktop size PCI Express graphics cards, wireless network interface cards, TV tuner cards, common access card (CAC) readers, and soundcards. Media remote control units are available that use the ExpressCard slot to store and recharge        Sony VAIO VGN-NR11Z/S Battery .

Standards

The Personal Computer Memory Card International Association (PCMCIA) developed both the ExpressCard standard and the PC Card standards. The host device supports both PCI Express and USB 2.0 connectivity through the ExpressCard slot; cards can be designed to use either mode      Sony VAIO VGN-NR11M/S Battery .

The cards are hot-pluggable. This is an open standard by ITU-T definition which can be obtained from the ExpressCard website. The documentation is free to members of PCMCIA, and US$2,500 to non-members as of 2009    Sony VAIO VGN-NR11Z/T Battery .

Form factors

The ExpressCard standard specifies two form factors, ExpressCard/34 (34 mm wide) and ExpressCard/54 (54 mm wide, in an L-shape)—the connector is the same on both (34 mm wide)       SONY VAIO VGN-FZ180E Battery .

Standard cards are 75 mm long (10.6 mm shorter than CardBus) and 5 mm thick, but may be thicker on sections that extend outside the standard form for antennas, sockets, etc.

The 34 mm slot accepts only 34 mm cards      SONY VAIO VGN-FZ220E Battery .

The 54 mm slot accepts both 34 mm and 54 mm cards. A diagonal guide in the rear of the 54 mm slot guides 34 mm cards to the connector. Adapters are available for connecting an ExpressCard/34 card to a CardBus (but not 16-bit PC Card) slot    SONY VAIO VGN-FZ340E Battery .

Comparison to other standards

The older PC Cards came in 16-bit and the later 32-bit CardBus designs. The major benefit of the ExpressCard over the PC card is more bandwidth, due to the ExpressCard's direct connection to the system bus over a PCI Express ×1 lane and USB 2.0, while CardBus cards only interface with PCI      SONY VAIO VGN-FZ430E Battery .

The ExpressCard has a maximum throughput of 2.5 Gbit/s through PCI Express and 480 Mbit/s through USB 2.0 dedicated for each slot, while all CardBus devices connected to a computer share a total 1.06 Gbit/s bandwidth.

The ExpressCard standard specifies voltages of either 1.5 V or 3.3 V; CardBus slots can use 3.3 V or 5.0 V   SONY VAIO VGN-FZ460E Battery .

The [ExpressCard FAQ claims lower cost, better scalability, and better integration with motherboard chipset technology than Cardbus. PCMCIA devices can be connected to an ExpressCard slot via an adapter          SONY VAIO VGN-FZ480E Battery .

When the PC Card was introduced, the only other way to connect peripherals to a laptop computer was via obsolescent RS232 and parallel ports of limited performance, so it was widely adopted for many peripherals. More recently, virtually all laptop equipment has 480 Mbit/s Hi-Speed USB 2.0 ports     SONY VAIO VGN-FZ4000 Battery ,

and most types of peripheral which formerly used a PC Card connection are available for USB, making the ExpressCard less necessary than the PC Card was in its day. Some laptop computers do not have an ExpressCard slot. For example, as of the second half of 2009 the only Apple laptop computer with an ExpressCard slot is the 17-inch MacBook Pro         SONY VAIO VGN-FZ31E Battery .

Availability

An ExpressCard slot had been commonly included on high-end laptops made since 2006, but has now been superseded by USB 3.0. According to the statement on the PCMCIA website, "The PCMCIA Association has been dissolved and the San Jose office closed  SONY VAIO VGN-FZ31B Battery .

All activities and Standards, including the ExpressCard Standard and PC Card Standard, will be managed going forward by the USB Implementer's Forum." The information below is out of date        SONY VAIO VGN-FZ31J Battery .

• Hewlett-Packard began shipping systems with ExpressCard in November 2004.
• Lenovo integrated the slot into their flagship ThinkPad T43 in May 2005         SONY VAIO VGN-FZ31M Battery .
• Dell Computer also incorporates this in their Precision (the 17 in models have them exclusively, the 15 in Precisions have both express card and PCMCIA Card slots), Inspiron, Latitude (Latitude D-series have PCMCIA card slots. The D820/D830 have both ExpressCard and PCMCIA card slots), Studio, Vostro and XPS Laptop product lines     SONY VAIO VGN-FZ31Z Battery .
• Fujitsu-Siemens began shipping systems with ExpressCard in mid 2005.
• Apple Inc. included single ExpressCard/34 slots in every MacBook Pro notebook computer from January 2006 through June 2009        SONY VAIO VGN-FZ38M Battery .
• At the June 8, 2009Apple Worldwide Developers Conference the company announced that the 15-inch and 13-inch MacBook Pro models would replace the ExpressCard slot with a Secure Digital card slot, while retaining the ExpressCard slot on the 17-inch model     SONY VGP-BPS8 Battery .
• ASUS has also replaced the PC Card slot with an ExpressCard slot on many of its new models.
• Sony also began shipping systems with ExpressCard with its new laptop VGN-SZ, VGN-NS, VPC and FW product line.
• The Acer Aspire laptop series also has a single ExpressCard/54 slot on most new models  SONY VGP-BPS13 Battery .
• Panasonic incorporates ExpressCard/54 slots in all the fully rugged and semi-rugged models of their Toughbook brand of laptop computers.
• Gateway notebooks (ML3109 and later) also ship with ExpressCard/54 interfaces   SONY VGP-BPS13/S Battery .

Because of the lack of backward compatibility, some laptop manufacturers have chosen to release models incorporating both CardBus (PCMCIA, PC Card) and ExpressCard slots. These include certain models of Acer Aspire, Toshiba Satellite, Dell Latitude and Precision, MSI S42x and Lenovo ThinkPad Z60m, R52, T60 and R61       SONY VGP-BPS13A/B Battery .

A large number of ExpressCard devices were presented at the CeBit trade show in Germany in March 2005. In November 2006, Belkin announced that it is launching the first ExpressCard docking station, which uses the PCIe part of an ExpressCard connection to enable 1600x1200 video and the USB part to provide USB, audio and network ports   SONY VGP-BPS13B/B Battery .

This points to the ability for ExpressCard to allow more capable non-OEM docking stations for laptop computers.

In 2007, Sony introduced its Vaio TZ model, which incorporates ExpressCards. Also the Sony Vaio FZ and Vaio Z series have the ExpressCard/34 Slot integrated in them     SONY VGP-BPS13A/S Battery .

Sony also uses the ExpressCard/34 form factor for the flash memory modules in its XDCAM EX/SxS based camcorders, making the copying of video data between these cameras and ExpressCard-equipped laptops easier. For this reason, Sony also offers a USB-based SxS reader for desktop computers    SONY VGP-BPS13AS Battery .

The new Toshiba Satellite P and X 200/205 series of laptops and desktop replacements have an ExpressCard/34 slot since April 2007.

ExpressCard 2.0

The ExpressCard 2.0 standard was delivered March 4, 2009 at CeBIT in Hannover    Dell Inspiron 1320n Battery .

It is expected to have a raw bandwidth of 5 Gbit/s (transfer speed 500 MB/s or 0.5 GB/s), which is ten times USB 2.0 (0.48 Gbit/s or 60 MB/s), and includes USB 3.0 (5.0 Gbit/s or 625 MB/s or 0.625 GB/s). It complies with PCI-Express 2.0 and SuperSpeed USB, which is part of the USB 3.0 specification       Dell Inspiron 1464 Battery .

It is backwards compatible with current ExpressCard modules and 2.0 ExpressCard modules will work in current slots. ExpressCard 2.0 products are expected to be in the market in late 2010.

CompactFlash (CF) is a mass storage device format used in portable electronic devices      Dell Inspiron 1564 Battery .

For storage, CompactFlash typically uses flash memory in a standardized enclosure.

The format was first specified and produced by SanDisk in 1994. The physical format is now used for a variety of devices  Dell Inspiron 1764 Battery .

CompactFlash became the most successful of the early memory card formats, outliving Miniature Card, SmartMedia, and PC Card Type I in mainstream popularity. The memory card formats that came out after the introduction of CompactFlash, such as SD/MMC, various Memory Stick formats, xD-Picture Card, offered stiff competition      Dell Studio 1450 Battery .

Most of these cards are significantly smaller than CompactFlash while offering comparable capacity and read/write speed. Proprietary memory card formats intended for use in the field of professional audio and video, such as P2 and SxS, are physically larger, faster, and significantly more expensive     Dell Studio 1457 Battery .

CompactFlash remains popular, and has even experienced something of a comeback. For example, in 2008 Sony chose CompactFlash as the recording media for use in the HVR-MRC1K tapeless video recorder instead of using smaller MemoryStick cards or expensive SxS cards    Dell Latitude D610 Battery .

In 2010 Canon chose CompactFlash as the recording media for use in its new lineup of professional high definition video cameras.

In November 2010, Sandisk, Sony and Nikon proposed a next generation card format targeted at high-definiton camcorders and high-resolution digital photo cameras         Toshiba NB100 Battery ;

not backward compatible, the proposed format would come in a similar form factor as CF/CFast but be based on PCI Express instead of ATA and would offer read speed of 500 MB/s and storage capabilities beyond 2 TiB. It remains unclear, if the CFA will adopt this proposal         Toshiba Satellite M65 battery ,

as CF 5.0 already supports media up to 128 PiB and CF 6.0 adds speeds up to 167 MB/s, while the SATA-based CFast already defines speeds up to 300 MB/s.

Description

There are two main subdivisions of CF cards, Type I (3.3 mm thick) and the thicker Type II (CF2) cards (5 mm thick)  Toshiba Satellite M60 battery .

The CF Type II slot is used byMicrodrives and some other devices, such as the Hasselblad CFV Digital Back for the Hasselblad series of medium format cameras. There are four main speeds of cards including the original CF, CF High Speed (using CF+/CF2.0), a faster CF 3.0 standard and a yet faster CF 4.0 standard that is being adopted as of 2007    Dell Latitude D830 Battery .

The thickness of the CF card type is dictated by the preceding PC Card standard.

CompactFlash was originally built around Intel's NOR-based flash memory, but has switched to NAND technology.CF is among the oldest and most successful formats, and has held a niche in the professional camera market especially well   Dell Latitude D620 Battery .

It has benefited from both a better cost to memory-size ratio than other formats, (for much of its life) and generally from greater available capacity than other formats.

CF cards can be used directly in a PC Card slot with a plug adapter, used as an ATA (IDE) or PCMCIA storage device with a passive adapter or with a reader, or attached to other types of ports such as USB or FireWire    Dell Inspiron Mini 10 Battery .

As some newer card types are smaller, they can be used directly in a CF card slot with an adapter. Formats that can be used this way include SD/MMC, Memory Stick Duo, xD-Picture Card in a Type I slot, and SmartMedia in a Type II slot, as of 2005. Some multi-card readers use CF for I/O as well     Sony VGN-FW11S Battery .

Flash memory, regardless of format, is limited to a finite number of erase/write cycles for any "block," before that block can no longer be written to successfully. Typically, the controller in a CompactFlash device attempts to prevent premature wear of a sector by choosing the write location for a piece of data so as to spread the writing over the device   Sony VGN-FW11M Battery .

This process is called wear leveling.

When using CompactFlash in ATA mode as a hard drive replacement, wear leveling becomes critical. The advanced CompactFlash controllers spread the wear-leveling across the entire drive allowing all blocks to participate   Sony VGN-FW139E/H battery .

The more advanced CompactFlash controllers will move data that rarely changes to ensure all blocks wear evenly.

Technical details

CompactFlash interface is a 50 pin subset of the 68 pin PCMCIA connector       Dell Latitude E5400 Battery .

"It can be easily slipped into a passive 68-pin PCMCIA Type II to CF Type I adapter that fully meets PCMCIA electrical and mechanical interface specifications."The Compactflash interface operates, depending on the state of a mode pin on powerup, as either 16-bit PC Card (0x7FF address limit) or as an IDE (PATA) interface       Dell Latitude E4200 Battery .

CompactFlash IDE mode defines an interface that is smaller than, but electrically identical to, the ATA interface. That is, it appears to the host device as if it were a hard disk. The CF device contains an ATA controller. CF devices operate at 3.3 volts or 5 volts, and can be swapped from system to system   Dell Inspiron 300M Battery .

CompactFlash supports C-H-S and 28-bit Logical block addressing (CF 5.0 introduced support for LBA-48). CF cards may be set to master or slave, but have issues sharing the IDE bus. CF cards with flash memory are able to cope with extremely rapid changes in temperature    Dell Vostro A840 Battery .

Industrial versions of flash memory cards can operate at a range of ?45 to +85 °C.

NOR-based flash has lower density than newer NAND-based systems, and CompactFlash is therefore the physically largest of the three memory card formats introduced in the early 1990s, being derived from the JEIDA/PCMCIA Memory Card formats   Dell Studio 1737 battery .

The other two are Miniature Card (MiniCard) andSmartMedia (SSFDC). However, CF did switch to NAND type memory later. The IBM Microdrive format implements the CF Type II interface, but is not solid-state memory. Hitachi and Seagate also make microdrives  Dell Inspiron E1505 battery .

Speed

CompactFlash IDE (ATA) emulation speed is usually specified in "x" ratings, e.g. 8x, 20x, 133x. This is the same system used for CD-ROMs and indicates the maximum transfer rate in the form of a multiplier based on the floppy disk, which is 150 KB/s   Dell RM791 battery .

, KB/sec

where R = transfer rate, K = speed rating. For example, 133x rating means transfer speed of: 133 * 150 kB/s = 19,950 kB/s ~ 20 MB/s.

These are manufacturer speed ratings. Actual transfer speed may be higher, or lower, than shown on the card depending on several factors   Dell XPS M1530 battery .

Solid State

For reads, the onboard controller first powers up the memory chips from standby. Reads are usually in parallel, error correction is done on the data, then transferred through the interface 16 bits at a time. Error checking is required due to soft read errors  Dell XPS M2010 battery .

Writes require powerup from standby, wear leveling calculation, a block erase of the area to be written to, ECC calculation, write itself (an individual memory cell read takes around 100 ns, a write to the chip takes 1ms+ or 10,000 times longer)   Acer Aspire One battery .

Since the USB 2.0 interface is limited to 60 MB/sec and lacks bus mastering hardware, USB implementation results in slower access.

A direct motherboard connection is often limited to 33 MB/sec because IDE to CF adapters lack high speed ATA (66 MB/sec plus) cable support. Power on from sleep/off takes longer than power up from standby        Toshiba Satellite P10 Battery .

Magnetic Media

Many 1-inch (25 mm) hard drives (often referred to by the trademarked name "Microdrive") typically spin at 3600 rpm so rotational latency is a consideration, as is spin-up from standby or idle. Seagate's 8 GB ST68022CF drive spins up fully within a few revolutions but power draw can reach up to 350 milliamps and runs at 40-50 mA average power   SONY VGN-FZ210CE Battery .

Its average seek time is 8 ms and can sustain 9 MB/s read and write, and has an interface speed of 33 MB/sec. Hitachi's 4 GB Microdrive is 12 ms seek, sustained 6 MB/sec.

Capacities and compatibility

Since flash memory is generally produced in capacities that are multiples of powers of 2, IEC standard binary prefixes are used throughout this article   Dell Precision M70 Battery .

The CF Specification (support 28 bit LBA) can support capacities up to 137 GB (128 GiB). Prior to 2006, CF drives using on magnetic media offered the highest capacities. But with the advent of 16 GiB and higher solid-state CF cards, they have offered the higher capacities    Toshiba Satellite L305 Battery .

Though, as of 2011, solid-state drives (SSDs) had supplanted both kinds of CF dives for large capacity requirements. Consequently, commercially available solid-state CF cards rarely go above 64 GiB, and 1-inch hard drives generally top out at 8 GiB       Toshiba Satellite T4900 Battery .

Solid State Capacities

SanDisk announced its 16 GiB Extreme III card at the Photokina trade fair, in September, 2006.That same month, Samsung announced 16, 32 and 64 GiB CF cards.Two years later, in September, 2008, Pretec announced 100GB cards      Toshiba PA3399U-2BRS battery .

Magnetic Media Capacities

Seagate announced a 5 GiB "1-inch hard drive" in June, 2004 , and an 8 GiB version in June, 2005.

Reliability

An important consideration for use in systems is reliability     Toshiba Satellite A200 Battery .

The original PC Card memory cards were battery backed RAM then NOR flash. At the time NOR flash had a write endurance of 10,000 cycles (but no read liability). The currently used NAND flash has an endurance of 1,000,000 writes per location (less reliable than magnetic media) before hard failure and is prone to frequent soft read errors       Toshiba Satellite 1200 Battery .

The CompactFlash card includes error checking and correcting (ECC) and wear leveling circuitry that is transparent to the user, although it may slow data access. Car PC Hacks suggests disabling Windows swap file and using its Enhanced Write Filter (EWF) to eliminate unnecessary writes to CF storage media        Toshiba Satellite M300 Battery .

However, EWF is available only in XP Embedded, not XP Professional, Home, or Media Editions versions of Windows.

Flash memory devices are non-volatile and solid-state, and thus are as, or more, robust than rotating media drives. The ST68022CF Microdrive is shock rated at 175G operating and 750G non-operating       SONY VGP-BPS13A/Q Battery .

Small cards consume around 5% of the power required by small disk drives and still have reasonable transfer rates of over 45 MB/s for the more expensive 'high speed' cards. Manufacturers warning on flash memory used for ReadyBoost indicates a current draw in excess of 500 mA     SONY VGP-BPS13A/Q Battery .

Filesystems

Originally, flash memory used Flash File System and JFFS to work around low level issues with the technology. Since hardware now hides much of the complexity from the end user, Compactflash disk storage for use in consumer devices is typically formatted as FAT12 (for media up to 16 MiB)        SONY VGP-BPS13B/Q Battery ,

FAT16 (for media up to 2 GiB, sometimes up to 4 GiB) and FAT32 (for media larger than 2 GiB) which not only works with end user computers but also is simple enough for limited processing ability of processors in devices such as cameras.

There are varying levels of compatibility among FAT32-compatible cameras, MP3 players, PDAs, and other devices  SONY VGP-BPS13B/Q Battery .

While any device that claims FAT32-capability should read and write to a FAT32-formatted card without problems, some devices are tripped up by cards larger than 2 GB that are completely unformatted, while others may take longer to apply a FAT32 format  SONY VGP-BPS13/Q Battery .

The way many digital cameras update the file system as they write to the card creates a FAT32 bottleneck. Writing to a FAT32-formatted card generally takes a little longer than writing to a FAT16-formatted card with similar performance capabilities   SONY VGP-BPS13/Q Battery .

For instance, the Canon EOS 10D writes the same photo to a FAT16-formatted 2 GB CompactFlash card somewhat faster than to a same speed 4 GB FAT32-formatted CompactFlash card, although the memory chips in both cards have the same write speed specification      SONY VGP-BPS21A/B Battery .

Although FAT16 is more wasteful of disk space with its larger clusters, it works better with the write strategy that flash memory chips require.

The cards themselves can of course be formatted with any type of file system such as JFS and NTFS  SONY VGP-BPS21/S Battery .

It can be divided into partitions as long as the host device can read them. CompactFlash cards are often used instead of hard drives in embedded systems, dumb terminals and various small form-factor PCs that are built for low noise output or power consumption  SONY VGP-BPS21B Battery .

CompactFlash cards are often more readily available and smaller than purpose-built solid-state drives and often have faster seek times than hard drives        SONY VGP-BPS21A Battery .

CF+ and Compact Flash specification revisions

When CompactFlash was first being standardized, even full-sized hard disks were rarely larger than 4 GB in size, and so the limitations of the ATA standard were considered acceptable        SONY VGP-BPS21 Battery .

However, CF cards manufactured after the original Revision 1.0 specification are available in capacities up to 128 GiB. While the current revision 6.0 works in [P]ATA mode, future revisions are expected to implement SATA mode          Sony VGP-BPS21A/B Battery .

• CompactFlash Revision 1.0 (1995), 8.3 MB/s (PIO mode 2), support for up to 128 GiB (137 GB) storage space.

• CompactFlash+ aka CompactFlash I/O (1997)        Sony VGP-BPS21/S Battery

• CF+ and CompactFlash Revision 2.0 (2003) added an increase in speed to 16.6 MB/s data-transfer (PIO mode 4). At the end of 2003, DMA 33 transfers were added as well, available since mid 2004       Sony VGP-BPS21B Battery .

• CF+ and CompactFlash Revision 3.0 (2004) added support for up to a 66 MB/s data transfer rate (UDMA 66), 25 MB/s in PC Card mode, added password protection, along with a number of other features. CFA recommends usage of the FAT32 filesystem for storage cards larger than 2 GiB          Sony VGP-BPS21A Battery .

• CF+ and CompactFlash Revision 4.0 (2006) added support for IDE Ultra DMA Mode 6 for a maximum data transfer rate of 133 MB/s (UDMA 133).

• CF+ and CompactFlash Revision 4.1 (2007) added support for Power Enhanced CF Storage Cards    Sony VGP-BPS21 Battery.

• CompactFlash Revision 5.0 (2010) added a number of features, including 48-bit addressing (supporting 128 Petabyte of storage), larger block transfers of up to 32 Megabytes, quality-of-service and video performance guarantees, and other enhancements  Sony Vaio PCG-5G2L Battery .

• CompactFlash Revision 6.0 (November 2010) added UltraDMA Mode 7 (167MB/s), ATA-8/ACS-2 sanitize command, TRIM and an optional card capability to report the operating temperature range of the card.

CE-ATA

CE-ATA is a Serial ATA interface based on the MultiMediaCard standard       Sony Vaio PCG-5G3L Battery . 

CFast

A variant of CompactFlash, known as CFast, is based on the Serial ATA bus, rather than the Parallel ATA/IDE bus all previous versions of CompactFlash are designed for            Sony Vaio PCG-5J1L Battery .

These cards support a higher maximum transfer rate than current CompactFlash cards. As of 2009, SATA (SATA II) supports transfer rates up to 300 MB/s while PATA is limited to 133 MB/s usingUDMA 6. Few, if any, current flash memory devices support speeds greater than 133 MB/s, but when enough are teamed together in parallel, they can exceed 300 MB/s  Sony Vaio PCG-5K2L Battery .

CFast cards are not physically or electrically compatible with CF cards, requiring new card readers and new digital cameras to take advantage of them. However, since SATA can emulate PATA on the software side, CFast cards don't require new driver software in operating systems    Sony Vaio PCG-5J2L Battery ,

but writing new drivers to use AHCI instead of PATA emulation will almost always result in significant performance gains. CFast cards use a 7-pin SATA data connector (identical to the standard SATA connector), but a 17-pin power connector that appears incompatible with the standard 15-pin SATA power connector,so an adaptor will be required to connect CFast cards in place of standard SATA hard drives      Sony Vaio PCG-5K1L Battery .

The first CFast cards reached the market in late 2009. At CES 2009, Pretec showed a 32 GB CFast and announced that they should reach market within a few months.

Type I and Type II

The only physical difference between the two types is that Type I devices are 3.3 mm thick while Type II devices are 5 mm thick  Sony Vaio PCG-5L1L Battery .

Electrically, the two interfaces are the same except that Type I devices are permitted to draw up to 70 mA supply current from the interface, while type II devices may draw up to 500 mA.

The vast majority of all Type II devices are Microdrives and other miniature hard drives       Sony Vaio PCG-6S2L Battery .

Flash based Type II devices are rare but a few examples do exist. Compact Flash — Secure Digital adapters usually are Type II. [31]Even the largest capacity cards commonly available are Type I cards. Most card readers will read both formats, with the exception of some early CF based cameras or poorer quality USB card readers where the slot is too small   Sony Vaio PCG-6S3L Battery .

Various manufacturers of 4 GB Compact Flash cards such as Sandisk, Toshiba, Alcotek and Hynix have developed devices that support mainly type I slots. Some of the latest DSLRs, like the Nikon D700, have also dropped Type II support   Sony Vaio PCG-6V1L Battery .

Microdrives

Microdrives are tiny hard disks—about 25 mm (1 inch) wide—packaged with a CompactFlash Type II form factor and interface. They were developed and released in 1999 by IBM with a capacity of 170MB       Sony Vaio PCG-6W1L Battery .

IBM sold its disk drive division, including the Microdrive trademark, to Hitachi in December 2002. There are now other brands of Microdrives (such as Seagate, Sony, etc.), and, over the years, these have become available in increasing capacities (up to 8 GB as of late 2008)        Sony Vaio PCG-6W2L Battery .

While these drives fit into and work in any CF II slot, the early versions drew more current (500 mA maximum) than flash memory (100 mA maximum). However current Microdrives use less than 200 mA for reads and writes (300 mA peak), and some flash devices used for high speed data e.g      Sony Vaio PCG-6W3L Battery .

Readyboost (memory can't power down to standby) draw more than the USB standard allows (500 mA). As they are mechanical devices, Microdrives are susceptible to damage from physical shock or temperature changes. However, Microdrives are not subject to the write cycle limitation inherent to flash memory      Sony Vaio PCG-7111L Battery .

The iPod mini, Nokia N91, iriver H10 (5 or 6 GB model), PalmOne LifeDrive, and Rio Carbon all used a CF Microdrive to store data.

Compared to other portable storage

• CF cards are considered more rugged and durable to many "in the field" photographic shocks, impacts and accidents   Sony Vaio PCG-7112L Battery .
• CompactFlash cards are capable of withstanding more physical damage in comparison to other, flimsier designs.

• Due to their compatibility with IDE/ATA they are used in many embedded systems as solid-state drives. In early 2008 the CFA demonstrated CompactFlash cards with a built in SATA interface       Sony Vaio PCG-7113L Battery .
• Several companies make adapters to allow CF cards to be connected to PCI, IDE, 44-pin laptop mini-IDE, and SATA connections, allowing a CF card to act as a solid-state drive with virtually any operating system or BIOS, and even in a RAID configuration      Sony Vaio PCG-7133L Battery .

• CompactFlash does not have any built in DRM or cryptographic features like on some USB flash drives and other card formats. The lack of such features contributes to the openness of the standard since other memory card standards with such features are subject to restrictive licensing agreements      Sony Vaio PCG-7Z2L Battery .

• CF cards are available at higher storage capacities than some smaller flash memory cards.

• CompactFlash lacks the mechanical write protection switch that some other devices have, as seen in a comparison of memory cards with exception of industrial CF-card models (AC60 Turbo/ AC73 and AC75 series) made by CoreSolid Storage   Sony Vaio PCG-8Y1L Battery .

• In the case of improper insertion, a card can potentially cause damage to the device receiving the card. However, this rarely happens as slots are usually designed to prevent this.

• CompactFlash's large dimensions in comparison to other cards limits its feasibility in very slim devices  Sony Vaio PCG-8Y2L Battery .
• The large card slot consumes devices' valuable internal space, especially in point and shootdigital cameras. On another hand, a CompactFlash card cannot be lost as easily as a tiny MicroSD card, and insertion and removal may be easier with a larger card  Sony Vaio PCG-8Z1L Battery .

Counterfeiting

There is extensive marketplace competition for sales of all brands of flash memory. As a result counterfeiting is quite widespread  Sony Vaio PCG-8Z2L Battery .

Under their own brand, or while imitating another, unscrupulous flash memory card manufacturers may sell low-capacity cards formatted to indicate a higher capacity, or else use types of memory that are not intended for extensive rewriting   Sony VAIO PCG-5G2L Battery .

The gigabyte (pronounced /?????ba?t/ GIG-?-byt) is a multiple of the unit byte for digital information storage. The prefix giga means 109 in theInternational System of Units (SI), therefore 1 gigabyte is 1000000000bytes. The unit symbol for the gigabyte is GBor Gbyte, but not Gb(lower case b) which is typically used for the gigabit        Sony VAIO PCG-5G3L Battery .

Historically, the term has also been used in some fields of computer science and information technology to denote the gibibyte, or1073741824 (10243 or 230) bytes. The Institute of Electrical and Electronics Engineers (IEEE) defined the unit accordingly for the use in power switchgear     Sony VAIO PCG-5J1L Battery .

In 2000, however, IEEE adopted the International Electrotechnical Commission (IEC) recommendation, which uses the metric prefix interpretation.

Today the usage of the unit gigabyte continues to depend on the context         Sony VAIO PCG-5K2L Battery .

When referring to disk storage capacities it usually means 109bytes.This also applies to data transmission quantities over telecommunication circuits, as the telecommunications and computer networking industries have always used the SI prefixes with their standards-based meaning        Sony VAIO PCG-5J2L Battery .

When referring to RAM sizes it most often (see binary prefix adoption) has a binary interpretation of 10243 bytes, i.e. as an alias for gibibyte. File systems and software often list file sizes or free space in some mixture of SI units and binary units; they sometimes use SI prefixes to refer to binary interpretation      Sony VAIO PCG-5K1L Battery

– that is using a label of gigabyte or GB for a number computed in terms of gibibytes (GiB), continuing the confusion.

In order to address this the International Electrotechnical Commission has been promoting the use of the term gibibyte for the binary definition      Sony VAIO PCG-5L1L Battery .

This position is endorsed by other standards organizations including the IEEE, the International Committee for Weights and Measures (CIPM) and the U.S. National Institute of Standards and Technology (NIST), but the binary prefixes have seen limited acceptance      Sony VAIO PCG-6S2L Battery .

The JEDEC industry consortium continues to recommend the IEEE 100 nomenclature of using the metric prefixes kilo, mega and giga in their binary interpretation for memory manufacturing designations.

Since the early 2000s most consumer hard drive capacities are grouped in certain size classes measured in gigabytes  Sony VAIO PCG-6S3L Battery .

The exact capacity of a given drive is usually some number above or below the class designation. Although most manufacturers of hard disk drives and flash-memory disk devices define 1 gigabyte as 1000000000bytes, software like Microsoft Windows reports size in gigabytes by dividing the total capacity in bytes by 1073741824   Sony VAIO PCG-6V1L Battery ,

while still reporting the result with the symbol "GB". This practice is a cause of confusion, as a hard disk with a manufacturer-rated capacity of 400 gigabytes might be reported by the operating system as only "372 GB", for instance. Other software, like Mac OS X 10.6 and some components of the Linux kernel  measure using the decimal units   Sony VAIO PCG-6W1L Battery .

The JEDEC memory standards uses the IEEE 100 nomenclatures which defines a gigabyte as 1073741824bytes (or 230 bytes).

The difference between units based on SI and binary prefixes increases as a semi-logarithmic (linear-log) function—for example, the SI kilobyte value is nearly 98% of the kibibyte, a megabyte is under 96% of a mebibyte   Sony VAIO PCG-6W2L Battery ,

and a gigabyte is just over 93% of a gibibyte value. This means that a 300 GB (279 GiB) hard disk is indicated only as 279 GB. As storage sizes increase and larger units are used, this difference becomes even more pronounced. Some legal challenges have been waged over this confusion such as a suit against Western Digital       Sony VAIO PCG-6W3L Battery .

Western Digital settled the challenge and added explicit disclaimers to products that the usable capacity may differ from the advertised capacity.

Because of its physical design, computer memory is addressed in multiples of base 2    Sony VAIO PCG-7111L Battery ,

thus, memory size at the hardware level can always be factored by a power of two. It is thus convenient to use binary units for non-disk memory devices at the hardware level, for example, in using DIMM memory boards. Software application, however, allocate memory  Sony VAIO PCG-7112L Battery ,

usually virtual memory in varying degrees of granularity as needed to fulfill data structure requirements, and binary multiples are usually not required. Other computer measurements, like storage hardware size, data transfer rates, clock speeds,operations per second, etc., do not depend on an inherent base, and are usually presented in decimal units      Sony VAIO PCG-7113L Battery.

The format has proven very popular and considered the de-facto industry standard, SD technology is used by more than 400 brands across dozens of product categories and in more than 8,000 models         (Dell Studio XPS 1640 Battery)         .

SDSC (Standard-Capacity) cards, typically called SD, have an official maximum capacity of 2 GB, though commercially available up to 4 GB. SDHC(High-Capacity) cards have a maximum capacity of 32 GB, and SDXC (eXtended-Capacity) cards have a maximum capacity of 2 TB      (Dell Vostro 1710 Battery)     .

Changes to the interface of the established format have made some older host devices, that were designed for standard SD cards, unable to handle the newer SDHC and SDXC families. All SD card families have the same physical shape, which tends to cause confusion with consumers, thus the SD Card Association has been trying to educate the public Dell KM958 battery .

History

In 1999, SanDisk, Matsushita, and Toshiba first agreed to develop and market the SD (Secure Digital) Memory Card, which was a development of the MMC. With a physical profile of 24×32×2.1 mm3, the new card provided both DRM up to the SDMI standard, and a high memory density for the time   Dell Studio 1555 battery .

The new format was designed to compete with Sony's Memory Stick format, which was released the previous year, and featured MagicGate DRM. It was mistakenly predicted that DRM features would be widely used due to pressure from music and other media suppliers to prevent piracy     Sony VGP-BPS13 battery .

The signature SD logo was actually developed for another use entirely: it was originally used for the Super Density Disc, which was the unsuccessful Toshiba entry in the DVD format war. This is why the D resembles an optical disc  Sony VGP-BPS13/B battery .

At the 2000 CES trade show Matsushita, SanDisk, and Toshiba Corporation announced the creation of the SD Card Association to promote SD cards. It is headquartered in California and its executive membership includes some 30 world-leading high-tech companies and major content companies   Sony VGP-BPS13/S battery .

Early samples of the SD Card were available in the first quarter of 2000, with production quantities of 32 and 64 megabytes available 3 months later.

In April 2006, the SD Association released a detailed specification for the non-security related parts of the SD Memory Card standard  Sony VGP-BPS13A/B battery .

The organization also released specifications for the SDIO (Secure Digital Input Output) cards and the standard SD host controller. During the same year, specifications were finalized for the small-form-factor microSD (formerly known as TransFlash) and SDHC, with capacities in excess of 2 GB and a minimum sustained read/write speed of 17.6 Mb/s Sony VGP-BPS13B/B battery .

In January 2009, the SD Association announced the SDXC family that will support cards up to 2 TB memory size and speeds up to 300 MBytes/sec.

Design and implementation

SD cards are based on the older MultiMediaCard (MMC) format, but have a number of differences   Sony VGP-BPL9 battery :

• The SD card is asymmetrically shaped in order not to be inserted upside down, while an MMC would go in most of the way but not make contact if inverted.
• SD cards are thicker than MMCs. SD cards generally measure 32 × 24 × 2.1 mm, but as with MMCs can be as slim as 1.4 mm if they lack a write-protect switch   Sony VGP-BPS13B/B battery ;
• such cards, called Thin SD, are described in the SD specification, but they are non-existent or rare in the market as most devices requiring a slimmer card use the smaller versions of SD: miniSD or microSD.
• The card's electrical contacts are recessed beneath the surface of the card, protecting them from contact with a user's fingers  Sony VGP-BPL15 battery .
• SD cards typically have transfer rates in the range of 80–160 Mb/s, but this is subject to grow, due to recent improvements to the MMC standard.

Devices with SD slots can use the slimmer MMCs, but standard SD cards will not fit into the slimmer MMC slots   Dell Inspiron E1505 battery .

miniSD cards can be used directly in SD slots with a simple passive adapter, since the cards differ in size and shape but not electrical interface. With an active electronic adapter, SD cards can be used in CompactFlash or PC card slots. Some SD cards include a USB connector for compatibility with desktop and laptop computers        Dell Latitude E6400 battery ,

and card readers allow SD cards to be accessed via connectivity ports such as USB, FireWire, and the parallel printer port. SD cards can also be accessed via a floppy disk drive with a FlashPath adapter.

Each SD card family are available in up to 3 physical sizes          HP Pavilion dv6000 Battery .

The SD and SDHC families are available in all 3 sizes, but the latest SDXC family is not available in the mini size.

Standard Size

• SD, SDHC, SDXC, SDIO
• 32 mm x 24 mm x 2.1 mm. The MMC and rare thin SD cards are 1.4mm thick       SONY VAIO VGN-FZ Battery .

Mini Size

• miniSD, miniSDHC, miniSDIO
• 21.5 mm x 20 mm x 1.4 mm.

Micro Size

• microSD, microSDHC, microSDXC          SONY VAIO VGN-FZ18 Battery
• 15 mm x 11 mm x 1.0 mm.

Optional write-protect tab

When looking at the card from the top (see pictures) there is one required notch on the right side (the side without the diagonal notched corner)          SONY VAIO VGN-FZ21E Battery .

On the left side may be a write-protection notch. If this is present, the card cannot be written. If the notch is covered by a sliding write protection tab, or absent, then the card is writeable. Because the notch is detected only by the reader, the protection can be overridden if desired (and if supported by the reader)        SONY VAIO VGN-FW21E Battery .

Not all devices support write protection, which is an optional feature of the SD standard.

Some SD cards have no write-protection notch, and it is absent completely in the microSD and miniSD formats   SONY VAIO VGN-NR11S/S Battery .

Some music and film media companies (e.g., Disney) have released limited catalogs of records and/or videos on SD. These usually contain DRM-encoded Windows Media files, making use of the SD format's DRM capabilities. Such media are usually permanently marked read-only by adding the notch with no tabs         SONY VAIO VGN-NR11M/S Battery .

File system

Like other flash card technologies, most SD cards ship preformatted with a file system on top of an MBR partition scheme. SD cards are typically formatted as FAT16, SDHC cards as FAT32, SDXC cards as exFAT         SONY VAIO VGN-NR11Z/S Battery .

The ubiquity of this file system allows the card to be accessed on virtually any host device with an SD reader. Also, standard FAT maintenance utilities (e.g., SCANDISK) can be used to repair or retrieve corrupted data, and some utilities can recover deleted files, providing that they have not been overwritten         SONY VAIO VGN-NR11Z/T Battery .

However, because the card appears as a removable hard drive to the host system, the card can be reformatted to any file system supported by the operating system. Conversely, an SD card can contain an embedded operating system (such as a Live USB) to recover a corrupted host computer by natively booting from the flash media reader  Sony VAIO VGN-FZ21E Battery .

SD cards with 4 GB and smaller capacities can be used with many systems by being formatted with FAT16 (4 GB only possible by using 64kiB clusters, and not widely supported) or FAT32 file system (common for file systems 4GB and bigger). Cards 4GB and bigger can only be formatted with a file system that can handle these storage sizes, such as FAT32         Sony VAIO VGN-FW21E Battery .

SD cards are plain block devices and do not in any way imply any specific partition layout or file system thus partition schemes other than MBR partitioning and the FAT file systems can be used. Under Unix-like operating systems such as Linux or FreeBSD, SD cards can be formatted using, for example, the UFS, EXT3 or the ReiserFS file systems         Sony VAIO VGN-NR11S/S Battery ;

under Mac OS X, SD cards can be partitioned as GUID devices and formatted with the HFS+ file system. Under MS-Windows and some unix systems, SD cards can be formatted using the NTFS and on later versions exFAT file system. However most consumer products will expect MBR partitioning and FAT16/FAT32 filesystem      Sony VAIO VGN-NR11Z/S Battery .

Fragmentation may slow down the effective write speed but the effect is tiny compared with that of fragmentation on hard drives. Defragmentation tools may be used. However, it is unnecessary to use any disk optimization tool because on an SD card the time required to access any block is the same          Sony VAIO VGN-NR11M/S Battery .

Defragmenting an SD card will wear the card out and is not normally recommended, as the number of writes, before failure occurs, is limited (often as few as 100,000 times).

Transfer modes

At the electrical level, SD supports at least three transfer modes: one-bit SD, four-bit SD, SPI           Sony VAIO VGN-NR11Z/T Battery .

All cards must support all three modes, except for microSD where SPI is optional. The cards must also support clock frequencies of up to 25 MHz for regular cards, and 50 MHz for high-speed cards.

One-bit SD

Separate command and data channels and a proprietary transfer format        SONY VAIO VGN-FZ180E Battery .

Four-bit SD

Uses extra pins plus some reassigned pins.

SPI

Serial Peripheral Interface Bus, a simpler subset of the SD protocol for use with microcontrollers. This mode is optional on microSD cards         SONY VAIO VGN-FZ220E Battery .

UHS-I

The Ultra High Speed mode is found exclusively on SDXC and SDHC products. SDXC or SDHC products with the UHS-I symbol are capable of supporting data transfer speeds up to 104 MB/s. UHS-I quadruples the extant top speed of 25 MB/s   SONY VAIO VGN-FZ340E Battery .

UHS bus interfaces are backwards compatible. SDXC UHS-I and SDHC UHS-I memory cards can achieve best performance when paired with a UHS-I device and are designed to allow consumers to record HD resolution videos, plus perform other simultaneous recording functions   SONY VAIO VGN-FZ430E Battery .

UHS-II

Available exclusively on SDXC and SDHC products. The standard raises the data transfer speed to a theoretical maximum of 312 MB/s.

DRM features

The digital rights management scheme embedded in the SD cards is defined as the Content Protection for Recordable Media (CPRM) by the 4C Entity and is centered around use of the Cryptomeria cipher (also known as C2)   SONY VAIO VGN-FZ460E Battery .

The specification is kept secret and is accessible only to licensees. This DRM has not been seen "in the wild" and few, if any, devices appear to provide support for it. DVD-Audio uses a very similar scheme known as Content Protection for Prerecorded Media (CPPM)  SONY VAIO VGN-FZ480E Battery .

If an SD card is inserted into a Windows Phone 7, it "locks the card to the phone with an automatically generated key" so that "the SD card cannot be read by another phone, device, or PC".Symbian devices, however, are some of the very few which can perform the necessary low-level format operations on locked SD cards    SONY VAIO VGN-FZ4000 Battery .

It is therefore possible to use a device such as the Nokia N8 to reformat the card for subsequent use in other devices.

Super*Talent, a manufacturer of computer memory, has created the Super Digital card. They are the same in appearance and function as regular Secure Digital cards, but they lack the CPRM code commonly found in Secure Digital cards  SONY VAIO VGN-FZ31E Battery .

Compared to other flash memory formats

Overall, SD is less open than CompactFlash or USB flash memory drives; these are open standards which can be implemented free of payment for licensing, royalties, or documentation  SONY VAIO VGN-FZ31B Battery .

(CompactFlash and USB flash drives may, however, require licensing fees for the use of associated logos and trademarks.)

However, SD is much more open than Memory Stick, for which no public documentation nor any documented legacy implementation is available   SONY VAIO VGN-FZ31J Battery .

All SD cards (other than microSD) can, at least, be accessed freely using the well-documented SPI/MMC mode.

xD cards are simply 18-pin NAND flash chips in a special package and support the standard command set for raw NAND flash access  SONY VAIO VGN-FZ31M Battery .

Although the raw hardware interface to xD cards is well understood, the layout of its memory contents—necessary for interoperability with xD card readers and digital cameras—is totally undocumented. The consortium that licenses xD cards has not released any technical information to the public        SONY VAIO VGN-FZ31Z Battery .

Speeds

There are different speeds of SD card available. The official unit of measurement is the Speed Class Rating; an older unit of measurement is the × rating.

Speed Class Rating

The Speed Class Rating is the official unit of speed measurement for SD Cards, defined by the SD Association  SONY VAIO VGN-FZ38M Battery .

The Class number represents a multiple of 8 Mb/s (1 MB/s), and meets the least sustained write speeds for a card in a fragmented state. These are the ratings of some currently available cards:

• Class 0 cards do not specify performance, which includes all legacy cards prior to class specifications SONY VGP-BPS8 Battery.
• Class 2, 2 MB/s, slowest for SDHC cards.
• Class 4, 4 MB/s.
• Class 6, 6 MB/s.
• Class 10, 10 MB/s       SONY VGP-BPS13 Battery .

Even though the class ratings are defined by a governing body, like × speed ratings, class speed ratings are quoted by the manufacturers and not verified by any independent evaluation process. In applications that require sustained write throughput, such as video recording, the device may not perform satisfactorily if the SD card's class rating falls below a particular speed  SONY VGP-BPS13/S Battery .

For example, acamcorder that is designed to record to class 6 media may suffer dropouts or corrupted video on slower media. On slower class cards, digital cameras may experience a lag of several seconds between photo-taking, whilst the camera writes the picture to the card   SONY VGP-BPS13A/B Battery .

Important differences between the Speed Class and the traditional CD-ROM drive speed measurement ("×" speed ratings) are that speed class:

1. may be queried by the host device;
2. defines the minimum transfer speed   SONY VGP-BPS13B/B Battery .

Since the class rating is readable by devices, they can issue a warning to the user if the inserted card's reported rating falls below the application's minimum requirement.

On 21 May 2009, Panasonic announced new class 10 SDHC cards, claiming that this new class is "part of SD Card Specification Ver.3.0"       SONY VGP-BPS13A/S Battery .

Toshiba also announced cards based on the new 3.0 spec.

On 1 June 2010, Pretec announced the new Class-16 HD-video grade SDXC 64GB card at Computex Taipei 2010   SONY VGP-BPS13AS Battery .

× rating

The × rating is equal to 1.2 Mb/s. It is derived from the standard CD-ROM drive speed of 1.2 Mb/s (approximately 150 kB/s). Basic cards transfer data up to six times (6×) the data rate of the standard CD-ROM speed (7.2 Mb/s vs 1.2 Mb/s)  Dell Inspiron 1320n Battery .

The 2.0 specification defines speeds up to 200×, but unlike the class rating system, does not mandate that ×-ratings measure the card's least sustained write-speed. So, typically, manufacturers provide ×-ratings based on maximum read/write speeds   Dell Inspiron 1464 Battery .

Furthermore, for most cards, the fastest read speed is typically swifter than its fastest write speed, leading some manufacturers to use read-speed as the ×-rating measurement. Other vendors, such as Kingston, use write-speed.

This table lists common ratings, the minimum transfer rates, and the corresponding Speed Class  Dell Inspiron 1564 Battery .

Like most memory card formats, SD is covered by numerous patents and trademarks.

Three versions of the SD specification have been set: 1.0, 1.1 and 2.0. These were originally available only after agreeing to a non-disclosure agreement (NDA) that prohibited development of an open source driver, which generated consternation in the open-source and free software communities     Dell Inspiron 1764 Battery .

However, the system was eventually reverse-engineered, and the non-DRMed sections of the memory cards could be accessed by free software drivers.

Since then, the SD Card Association (SDA) has made access to a simplified version of the specification available under a less restrictive license     Dell Studio 1450 Battery .

Although most open-source drivers were written before this, it has helped them to solve some compatibility issues.

In 2006, the SD Card Association also released a simplified version of their host controller interface specification (not to be confused with the physical specification, which covers the actual cards and their protocol        Dell Studio 1457 Battery )

and later also for physical layer, ASSD extensions, SDIO and SDIO Bluetooth Type-A specifications under a disclaimers agreement.Like the physical specification, most of the information had already been discovered before the public release and at least Linux had a fully free driver for it   Dell Latitude D610 Battery .

Still, building a chip conforming to this specification caused the One Laptop per Child project to claim "the first truly Open Source SD implementation, with no need to obtain an SDI license or sign NDAs to create SD drivers or applications    Toshiba NB100 Battery ."

For the most part, the lack of a complete, open SD specification mainly affects embedded systems and laptop systems, since desktop users generally read SD cards via USB-based card readers. These card readers present a standard USB mass storage interface to memory cards, thus separating the operating system from the details of the underlying SD interface  Toshiba Satellite M65 battery .

However, embedded systems (such as portable music players) usually access SD cards directly, and therefore complete programming information is necessary. Desktop card readers are themselves examples of such embedded systems; the manufacturers of these readers have usually paid the SDCA for complete access to the SD specifications  Toshiba Satellite M60 battery .

Many notebook computers now include SD card readers not based on USB; device drivers for these essentially access the SD card directly, as in embedded systems.

Royalties for SD/SDIO licences are imposed for manufacture and sale of memory cards and host adapters  Dell Latitude D830 Battery

(USD$1,000/year plus membership at USD$1,500/year) but SDIO cards can be made without royalties and MMC host adapters do not require a royalty. MMCs have a seven-pin interface; SD and SDIO have expanded this to nine pins and MMC Plus expands this even further with thirteen pins       Dell Latitude D620 Battery .

Types of MMC/SD cards

The SD card is not the only flash memory card standard ratified by the Secure Digital Card Association (SDCA). Other SD Card Association formats include miniSD, microSD (formerly known asTransFlash before ratification by the SD Card Association)   Dell Inspiron Mini 10 Battery ,

and SDHC (Secure Digital High Capacity, for capacities above 4 GB–although, there are some card readers that cannot handle over 1 GB that are not SDHC). SDHC is not fully compatible with the format that it extends, in that SD devices that do not specifically support SDHC will not work with the newer cards       Sony VGN-FW11S Battery .

The smaller miniSD and microSD cards are usable in full size MMC/SD/SDIO slots with an adapter (which must route the electrical connections as well as making physical contact). However, it is already difficult to create I/O devices in the SD form factor and this will be even more difficult in the smaller sizes           Sony VGN-FW11M Battery .

As SD slots still support MMCs, the separately-evolved smaller MMC variants are also compatible with SD-supporting devices. Unlike miniSD and microSD (which are sufficiently different from SD to make mechanical adapters necessary), RS-MMC slots maintain backward compatibility with full-sized MMCs, because the RS-MMCs are simply shorter MMCs    Sony VGN-FW139E/H battery .

More information on these variants can be found in the article about the MultiMediaCard standard.

It is also important to note, that unlike for data storage (which typically works everywhere an SD slot is present)   Dell Latitude E5400 Battery ,

an SDIO device must be supported and equipped with drivers and applications for the host system and usually does not work outside of the manufacturer's scope (which means, for example, that an HP SDIO camera usually does not work with PDAs for which it is not listed as an accessory)         Dell Latitude E4200 Battery .

This behavior is often not expected by end users who typically expect that only the SD slot is required. Similar compatibility issues are sometimes seen with Bluetooth devices, although to a much lesser extent thanks to standardized Bluetooth profiles   Dell Inspiron 300M Battery .

Most, possibly all, current MMC flash memory cards support SPI mode even if not officially required as failure to do so would severely affect compatibility. All cards currently made by SanDisk,Ritek/Ridata, and Kingmax digital appear to support SPI  Dell Vostro A840 Battery .

Also, MMCs may be electrically identical to SD cards but in a thinner package and with an electronic fuse blown to disable SD functionality (so no SD royalties need to be paid). Some microSD cards do not support SPI mode.

MMC defined the SPI and one-bit MMC/SD protocols          Dell Studio 1737 battery .

The underlying SPI protocol has existed for years as a standard feature on many microcontrollers. The new protocol used open collector signaling to allow multiple cards on the same bus but this actually causes problems at higher clock rates      Dell Inspiron E1505 battery .

While SPI used three shared lines plus a separate chip select to each card, the new protocol allows up to 30 cards to be connected to the same three wires (with no chip select) at the expense of a much more complicated card initialization and the requirement that each card have a unique serial number for plug and play operation       Dell RM791 battery ;

this feature is rarely used and its use is actively discouraged in new standards (which recommend a completely separate channel to each card) because of speed and power consumption issues. The quasi-proprietary one-bit protocol was extended to support four bit wide (SD and MMC) and eight bit (MMC only)        Dell XPS M1530 battery

transfers for more speed while much of the rest of the computer industry is moving to higher speed narrower channels; standard SPI could simply have been clocked at higher data rates (such as 133 MHz) for higher performance than offered by four-bit SD      Dell XPS M2010 battery

— embedded CPUs that did not already have higher clock rates available would not have been fast enough to handle the higher data rates anyway. The SD card association dropped support for some of the old one-bit MMC protocol commands and added support for additional commands related to copy protection       Acer Aspire One battery .

Standard-SD cards (non-SDHC) with greater than 1 GB capacity

The SD Card Association's current specifications define how a standard SD (non-SDHC) card with more than 1 GB and up to 4 GB capacity should be designed         Toshiba Satellite P10 Battery .

These cards should be readable in any SD 1.01 devices that take the block length data into account. Any 1 GB or lesser card should always work (so the key question is how one's reader handles block length).

According to the specification, the maximum capacity of a standard SD card is defined by (BLOCKNR × BLOCK_LEN), where BLOCKNR may be (4,096 × 512) and BLOCK_LEN may be up to 2,048        SONY VGN-FZ210CE Battery .

This allows a capacity of 4 GB. The main problem is that some of the card readers support only a block (or, sector) size of 512 bytes, so greater than 1 GB non-SDHC cards may cause compatibility difficulties for users of such devices.

Compatibility issues with 4 GB and larger cards

Devices that use SD cards identify the card by requesting a 128-bit identification string from the card       Dell Precision M70 Battery .

For standard-capacity SD cards, 12 of the bits are used to identify the number of memory clusters (ranging from 1 to 4,096) and 3 of the bits are used to identify the number of blocks per cluster (which decode to 4, 8, 16, 32, 64, 128, 256, or 512 blocks per cluster)  Toshiba Satellite L305 Battery .

In older 1.x implementations the standard capacity block was exactly 512 bytes. This gives 4,096 × 512 × 512 = 1 gigabyte of storage memory. A later revision of the 1.x standard allowed a 4-bit field to indicate 1,024 or 2,048 bytes per block instead, yielding up to 4 gigabytes of memory storage   Toshiba Satellite T4900 Battery .

Devices designed before this change may incorrectly identify such cards, usually by misidentifying a card with lower capacity than is the case by assuming 512 bytes per block rather than 1,024 or 2,048.

For the new SDHC (2.0) implementation, 32 bits of the identification string are used to indicate the memory size in increments of 512 bytes       Toshiba PA3399U-2BRS battery .

The SDCA currently allows only 26 of the 32 bits to be used, giving a maximum size of 32 GB. All SD cards with a capacity larger than 4 GB must use the 2.0 implementation at minimum. Two bits that were previously reserved and fixed at 0 are now used for identifying the type of card, 0: standard; 1: SDHC; 2, 3: reserved      Toshiba Satellite A200 Battery .

Non-SDHC devices are not programmed to read this code and therefore cannot correctly identify SDHC or SDXC cards.

All SDHC readers work with standard SD cards.

Many older devices will not accept the 2 or 4 GB size even though it is in the revised standard   Toshiba Satellite 1200 Battery .

The following statement is from the SD Card Association specification:

To make 2 GByte card, the Maximum Block Length (READ_BL_LEN=WRITE_BL_LEN) shall be set to 1024 bytes. However, the Block Length, set by CMD16, shall be up to 512 bytes to keep consistency with 512 bytes Maximum Block Length cards (Less than and equal 2 Gbyte cards)        Toshiba Satellite M300 Battery .

Storage capacity calculations

SD cards contain a Card-Specific Data (CSD) register which holds the card's capacity, among many other things. The format changed considerably between version 1.0 (SD) and version 2.0 (SDHC, SDXC), this is the cause of the incompatibility between SD and newer cards    SONY VGP-BPS13A/Q Battery .

CSD v2.0 expanded the C_SIZE register, removed the C_SIZE_MULT register, and no longer uses READ_BL_LEN for capacity calculation.Capacity is calculated thus:

CSD Version 1.0  SONY VGP-BPS13A/Q Battery :

Capacity=(C_SIZE+1)<<(C_SIZE_MULT+2)<<READ_BL_LEN 2GiB max.

Where 0<=C_SIZE<=4095, 0<=C_SIZE_MULT<=7, READ_BL_LEN==9 || READ_BL_LEN==10

CSD Version 2.0  SONY VGP-BPS13B/Q Battery :

Capacity=(C_SIZE+1)*524288

where for SDHC       4112<=C_SIZE<=65375 (approx. 2GB) < capacity < 32GiB

for SDXC       65535<=C_SIZE                        32GiB <= capacity <= 2TiB max.  SONY VGP-BPS13B/Q Battery

SDHC cards with greater than 32 GB capacity

Similarly to the above, as of version 2.00 of the specification,the capacity of an SDHC card is limited to 32 GB. However, while not strictly adhering to that standard, it is in principle possible to create SDHC-like cards of up to 2 TB capacity  SONY VGP-BPS13/Q Battery .

Some SDHC devices will accept SDXC cards with capacities greater than 32GB and recognize the full capacity, however compatibility is not guaranteed in all cases. SDHC cards have a fixed sector size of 512 bytes.

SDHC

SDHC (Secure Digital High Capacity, SD 2.0) is an extension of the SD standard which increases card's storage capacity up to 32 GBSONY VGP-BPS13/Q Battery .

SDHC cards share the same physical and electrical form factor as older (SD 1.x) cards, allowing SDHC-devices to support both newer SDHC cards and older SD-cards. To increase addressable storage, SDHC uses sector addressing instead of byte addressing as in the previous SD standard   SONY VGP-BPS21A/B Battery .

Byte addressing supported card capacities up to 4 GB, whereas sector addressing can theoretically support capacities up to 2 TB (2048 GB). The current standard limits the maximum capacity of an SDHC card to 32 GB  (it is expected that the SDHC specification will be revised in the future to allow card capacities greater than 32 GB)      SONY VGP-BPS21/S Battery .

SDHC cards will not work in devices designed to the older SD 1.x specification. The SDHC trademark is licensed to ensure compatibility.

SD and SDHC compatibility issues

The SDHC specification was completed in June 2006,but by that time, non-standard high-capacity (>1GB) SD cards (based on the older 1.x specification) were already on the market         SONY VGP-BPS21B Battery .

The two types of storage cards were not interchangeable, creating some confusion among customers. SD and SDHC cards and devices have these compatibility issues :

• Devices that do not specifically support SDHC do not recognize SDHC memory cards. Some devices can support SDHC through a firmware upgrade        SONY VGP-BPS21A Battery .
• SDHC devices are backward compatible with SD memory cards.
• Some manufacturers have produced 4 GB SD cards that conform to neither the SD2.0/SDHC spec nor existing SD devices  SONY VGP-BPS21 Battery .
• File System: SD cards are typically formatted with the FAT16 file system, while SDHC cards are typically formatted as FAT32. However, both types of cards can support other general-purpose file systems, such as UFS2, ext2 or the proprietary exFAT for example      Sony VGP-BPS21A/B Battery .
• Microsoft Windows may need a hotfix to support accessing SDHC cards.

SDXC

The Secure Digital Extended Capacity (SDXC) format was unveiled at CES 2009 (January 7–10, 2009). The maximum capacity defined for SDXC cards is 2 TB (2048 GB)       Sony VGP-BPS21/S Battery .

The older SDHC cards also have a maximum capacity of 2 TB based on the card data structures, but this is artificially limited to 32 GB by the SD 2.0 specification. The first SDXCs being released are governed by an SD 3.0 specification (which also still specifies FAT32 and thus lower capacities)         Sony VGP-BPS21B Battery ,

whereas higher capacity and faster SDXCs are expected to follow an SD 4.0 specification, which was due to be released in spring of 2010.

The maximum transfer rate of SDXCs which follow the SD 3.0 specification was announced as 832 Mbit/s (these are called UHS104speeds), with plans that the SD 4.0 specification shall increase this to 2.4 Gbit/s  Sony VGP-BPS21A Battery .

The SDcard association selected Microsoft's proprietary exFAT file system in the official SDXC specification; however, as with SD and SDHC, it is still a plain block device and thus arbitrary partitioning and other file systems can be used, such as FAT32, NTFS, ext2, UFS, etc       Sony VGP-BPS21 Battery .

History

On January 7, 2009, SanDisk and Sony announced the joint development of the XC variant of the competing Memory Stick format, boasting the same 2 TB maximum capacity of SDXC.

On January 8, 2009, Panasonic announced plans for production of 64 GB SDXC cards  Sony Vaio PCG-5G2L Battery .

On March 6, 2009, Pretec introduced the world's first SDXC card with a capacity of 32 GB and a read/write speed of 400 Mbit/s. At the introduction, there were no products compatible with the new memory card.

On August 3, 2009, Toshiba announced it will launch the world's first 64 GB SDXC Memory Card  with a read speed of 480 Mbit/sSony Vaio PCG-5G3L Battery .

The 64GB card (THNSU064GAA2BC) was planned to be available in the spring of 2010.  Toshiba card was available from April 13.

On January 6, 2010, Panasonic announced its first SDXC cards with 64GB and 48GB to be available in February (RP-SDW64GE1K and RP-SDW48GE1K)      Sony Vaio PCG-5J1L Battery .

On January 6, 2010, Sony announced the launch of Handycam HDR-CX55V with SDXC support.

On February 8, 2010, Canon announced the launch of the new EOS Rebel T2i Digital SLR camera, the first EOS model to support SDXC memory cards        Sony Vaio PCG-5K2L Battery .

On February 19, 2010, Panasonic launched in Japan World's first available for consumers SDXC memory cards with 64GB and 48GB (RP-SDW64GE1K and RP-SDW48GE1K) together with USB card readers compatible with SDXC format.

On February 22, 2010, SanDisk launched its 64GB SanDisk Ultra SDXC card        Sony Vaio PCG-5J2L Battery .

The first integrated SDXC card readers are available from JMicron and are expected to be used in laptops in 2010.

SDHC and SDXC compatibility issues

In the 3.0 specification, the electronic interface of SDHC and SDXC cards is the same. This means that SDHC hosts which have drivers which recognize the newly used capability bits, and have operating system software which understands the exFAT filesystem, are compatible with SDXC cards       Sony Vaio PCG-5K1L Battery .

The decision to label cards with a capacity greater than 32GB as SDXC and to use a different filesystem is due solely to the limitations in creating larger filesystems in certain versions of Microsoft Windows. Other operating systems, such as Linux, make no distinction between SDHC and SDXC cards, as long as the card contains a compatible filesystem   Sony Vaio PCG-5L1L Battery .

SDHC and SDXC cards and hosts have these compatibility issues:

• SDHC hosts will only support the SDXC cards which use UHS104 speeds;<  SDHC hosts will not recognize the SDXC cards which use the faster (SD 4.0), final specification of SDXC.
• SDXC hosts are backward compatible with SD and SDHC memory cards      Sony Vaio PCG-6S2L Battery .
• The operating systems that currently support SDXC are: Linux (with a proprietary driver for the exFAT filesystem ), Microsoft Windows 7, Windows Vista SP1+, Windows XP SP2 or SP3 with KB955704,  Windows Server 2008 SP1+, Windows Server 2003 SP2 or SP3 with KB955704, Windows CE 6+, and Mac OS X Snow Leopard (Intel-based)   Sony Vaio PCG-6S3L Battery .

SDIO

A SDIO (Secure Digital Input Output) card is a combination of an SD card and an I/O device. This kind of combination is increasingly found in portable electronics devices   Sony Vaio PCG-6V1L Battery .

Hosts that support SDIO (typically PDAs like the Palm Treo, but occasionally laptops or mobile phones) can use small hosts designed for the SD form factor, like GPS receivers, Wi-Fi or Bluetooth adapters, modems, Ethernet adapters, barcode readers, IrDA adapters, FM radio tuners, TV tuners, RFID readers,digital cameras, or other mass storage media such as hard drives  Sony Vaio PCG-6W1L Battery .

A number of other devices have been proposed but not yet implemented, including RS-232 serial adapters, fingerprint scanners, SDIO to USB host/slave adapters (which would allow an SDIO-equipped handheld device to use USB peripherals and/or interface to PCs), magnetic strip readers  Sony Vaio PCG-6W2L Battery ,

combinationBluetooth/Wi-Fi/GPS transceivers, cellular modems (PCS, CDPD, GSM, etc.), and APRS/TNC adapters.

SDIO cards are fully compatible with the SD Memory Card host controller (including mechanical, electrical, power, signaling, and software)      Sony Vaio PCG-6W3L Battery .

When an SDIO card is inserted into a non SDIO-aware host, it will cause no physical damage or disruption to device or host controller. SPI bus topology is mandatory for SDIO, unlike SD Memory. Most of the SD Memory commands are supported in SDIO  Sony Vaio PCG-7111L Battery .

SDIO cards can contain 8 separate logical cards, although currently, this is at most a memory and IO function. SD slots will take SD cards only. SDIO slots will take SD cards and SDIO cards.

SD cards with extra features

Various manufacturers have tried to make their SD cards stand out from the crowd in different ways  Sony Vaio PCG-7112L Battery

• SD Plus - A type of SD card made by Sandisk that has an integrated USB connector so it can be plugged directly into a USB port without needing any special card reader. This concept has proven successful and other companies started introducing similar designs branded as duo SD or 3 Way in the case of A-DATA's microSDHC to SDHC and USB all-in-one product  Sony Vaio PCG-7113L Battery ,
• which was available in 2008 only.
• Capacity Display - In 2006, A-DATA announced an SD card with its own digital display that would show how much free space is left on the card     Sony Vaio PCG-7133L Battery .
• Eye-Fi, Inc. - Produces an SD card with Wi-Fi capability built in for 802.11g, 802.11b, and backwards-compatible 802.11n wireless networks and supporting static WEP 40; 104; and 128, WPA-PSK, and WPA2-PSK security standards. The card works with any digital camera with an SD slot and can transmit captured images over a wireless network Sony Vaio PCG-7Z2L Battery.
• When not in range of a wireless network connection, the card makes use of its 2 GB capacity (EYE-FI-2 GB model) until the images can be transferred. Some models geotag their pictures.
• Gruvi - A rare type of microSD card with extra DRM features  Sony Vaio PCG-8Y1L Battery

Pre-Loaded Content

Towards the end of 2000s many manufacturers saw the need to distinguish their SD cards from one another. One idea was to introduce pre-loaded content onto new SD cards.

SanDisk introduced their SlotMusic which enabled users to buy digital music files already loaded onto their cards Sony Vaio PCG-8Y2L Battery .

Market penetration

Secure Digital cards are ubiquitous in consumer electronic devices, and have become the dominant means of storing several gigabytes of data in a small size       Sony Vaio PCG-8Z1L Battery .

Devices such as netbooks, digital cameras, camcorders, PDAs, mobile phones, video game consoles and digital audio players as well as many others use them.

Smaller devices tend to use microSD or miniSD rather than full sized SD cards       Sony Vaio PCG-8Z2L Battery .

SD cards are not generally used in mass produced devices where only a small amount of storage is needed due to economic reasons, or where a very large amount of storage is required.

Digital cameras

SD/MMC cards have replaced Toshiba's SmartMedia as the dominant memory card format used in digital cameras  Sony VAIO PCG-5G2L Battery .

In 2001, SmartMedia had achieved nearly 50% use, but by 2005 SD/MMC had achieved over 40% of the digital camera market and SmartMedia's share had plummeted, with cards not being easily available in 2007.

At this time all the leading digital camera manufacturers use SD in their consumer product lines      Sony VAIO PCG-5G3L Battery , including Canon, Casio, Fujifilm, Kodak, Nikon, Olympus, Panasonic, Pentax, Ricoh, Samsung, andSony. Previously, Olympus and Fujifilm used xD cards exclusively, while Sony only used Memory Stick. As of January 2010, they have added SD functionality to all models released since then      Sony VAIO PCG-5J1L Battery .

Some prosumer and professional camera models continue to offer CompactFlash, either on a second card slot or as the only storage, as it has historically offered a better price/capacity ratio and faster transfer rates       Sony VAIO PCG-5K2L Battery .

Embedded systems

Unlike CompactFlash, none of the SD card variants supports ATA signaling, limiting their use as solid state drives unless a separate converter chip is used. Although embedded systems exist that use SD cards as their main storage mechanism, a special SD controller chip is often used        Sony VAIO PCG-5J2L Battery .

In September 2008, the SD Card Association announced the Embedded SD standard to be released in November.

A homebrew hardware hack has brought SD card support to the popular Linksys WRT54G router by utilizing spare GPIO pins on the router's processor and the Linux kernel's MMC module. Transfer speeds of 1.6 Mbit/s can be achieved with this setup  Sony VAIO PCG-5K1L Battery .

P2 (P2 is short form for "Professional Plug-In") is a professional digital video storage media format introduced by Panasonic in 2004, and especially tailored toENG applications. It features tapeless (non-linear) recording of DVCPRO, DVCPRO50, DVCPRO-HD, or AVC-Intra streams on a solid state flash memorycard       Sony VAIO PCG-5L1L Battery .

The P2 Card is essentially a RAID of SD memory cards with an LSI controller tightly packaged in a die-cast PC card (formerly PCMCIA) enclosure, so data transfer rate increases as memory capacity increases. The system includes cameras, decks as drop-in replacement for VCRs, and a special 5.25" computer drive for random access integration with NLE systems  Sony VAIO PCG-6S2L Battery .

The cards can also be used directly where a PC card slot is available, as in most notebook computers, as a normal disk drive, although a custom software driver must first be loaded.

As of early 2010, P2 cards are available in capacities of 4, 8, 16, 32GB and 64GB       Sony VAIO PCG-6S3L Battery .

At introduction, P2 cards offered low recording capacity compared to competing, videotape-based formats (a miniDV tape holds roughly 13GB of data, and an S-size HDCAM tape holds 50GB). To solve this, camcorders and decks using P2 media employ multiple card slots, with the ability to span the recording over all slots        Sony VAIO PCG-6V1L Battery .

Cards are recorded in sequence, and when a card is full, it can be swapped out while another card is recording. This limits recording time only by power supply and the available amount of cards. If a card is partially full, the deck will record only until it is full. Unlike tape, old video cannot be recorded over accidentally. Old footage must be manually deleted   Sony VAIO PCG-6W1L Battery .

P2 cards are of a ruggedized PCMCIA type with the fastest transfer speeds currently available through this format. The card also contains a processor that organises and safeguards the files and the case is developed and crafted to "military" (according to Panasonic) specifications, making P2 cards tough and reliable  Sony VAIO PCG-6W2L Battery .     .

The first pieces of equipment released by Panasonic which use the P2 format included the AJ-SPX800 (a 2/3" broadcast camcorder for ENG and EFP applictions), the studio recorder AJ-SPD850, the AJ-PCD10 offload device (basically, a five-slot PC card reader with USB interface designed to fit a 5-1/4" IT systems bay)  Sony VAIO PCG-6W3L Battery ,

and the memory cards themselves - AJ-P2C004 (4 GB) and AJ-P2C002 (2 GB). Panasonic is currently shipping a wide range of camcorders that support the P2 format, including the professional AG-HVX200 HD handheld camcorder, and the high-end, or broadcast professional shoulder-mount AG-HPX500, AJ-HPX2000, and AJ-HPX3000 camcorders  Sony VAIO PCG-7111L Battery .

Panasonic has also announced the P2-based AG-HPX170 handheld HD camcorder. The HPX170 is very similar to the HVX200and the HVX200A, the main difference being the lack of a tape drive on the 170. The latest products to feature P2 technology are the well-received  recently launched AJ-HPX2700 and AH-HPX3700 "Varicam" high end cameras   Sony VAIO PCG-7112L Battery .

Specifications

• File format: MXF
• Maximum datarate: 800 Mbit/s
• Available sizes: 2 GB, 4 GB, 8 GB, 16GB, 32GB, 64GB
• Form factor: PC card (PCMCIA) type II   Sony VAIO PCG-7113L Battery

P2 Workflow

P2 is a solid state technology, and as such departs from the older method of recording video onto tape. Since the video output is saved onto a solid state P2 memory card as a file, many possibilities are opened up to change the approach to workflow  Sony VAIO PCG-7133L Battery ;

indeed, it is claimed that the workflow can be sped up and made more reliable, which in turn, reduces production costs . Since its inception, the development of this workflow, together with partners such as Avid and Apple, has matured, and has been adopted by many major production teams   Sony VAIO PCG-7Z1L Battery .

However for many in the post production field the P2 format is quite troublesome. Because no hard copy is produced from the camera, editors must rely on massive amounts of stable drive space for security. The raw files on the card are usually treated as the 'tape', and then the converted Quicktime files are treated as capture    Sony VAIO PCG-7Z2L Battery .

P2 is still seen in the production world as a maturing format, since storage media is so costly, and little has been done to address archiving tapeless productions.

The SD Card Association develops and publishes technical standards for SD Card technology, and promotes the use of the technology   Sony VAIO PCG-8Y1L Battery .

SD Cards are compactdata storage devices used to store digital files, such as picture files recorded by digital cameras. The association was founded on 28 January 2000 by Matsushita Electric Industrial Co., Ltd. (Panasonic), SanDisk Corporation and Toshiba Corporation     Sony VAIO PCG-8Y2L Battery.

It encompasses various types of fixed, mobile, and portable two-way radios, cellular telephones, personal digital assistants (PDAs), and wireless networking. Other examples of wireless technology include GPS units, garage door openers and or garage doors, wireless computer mice, keyboards and headsets,satellite television and cordless telephones (Dell Studio XPS 1640 Battery)  .

Wireless operations permits services, such as long range communications, that are impossible or impractical to implement with the use of wires. The term is commonly used in the telecommunications industry to refer to telecommunications systems (e.g. radio transmitters and receivers, remote controls, computer networks, network terminals, etc   (Dell Vostro 1710 Battery)      .

which use some form of energy (e.g. radio frequency (RF), infrared light, laser light, visible light, acoustic energy, etc.) to transfer information without the use of wires. Information is transferred in this manner over both short and long distances   Dell KM958 battery .

he term "wireless" has become a generic and all-encompassing word used to describe communications in which electromagnetic waves or RF (rather than some form of wire) carry a signal over part or the entire communication path. Common examples of wireless equipment in use today include  Dell Studio 1555 battery :

• Professional LMR (Land Mobile Radio) and SMR (Specialized Mobile Radio) typically used by business, industrial and Public Safety entities.
• Consumer Two way radio including FRS Family Radio Service, GMRS (General Mobile Radio Service) and Citizens band ("CB") radios  Sony VGP-BPS13 battery .
• The Amateur Radio Service (Ham radio).
• Consumer and professional Marine VHF radios.
• Cellular telephones and pagers: provide connectivity for portable and mobile applications, both personal and business  Sony VGP-BPS13/B battery .
• Global Positioning System (GPS): allows drivers of cars and trucks, captains of boats and ships, and pilots of aircraft to ascertain their location anywhere on earth.
• Cordless computer peripherals: the cordless mouse is a common example; keyboards and printers can also be linked to a computer via wireless        Sony VGP-BPS13/S battery .
• Cordless telephone sets: these are limited-range devices, not to be confused with cell phones.
• Satellite television: Is broadcast from satellites in geostationary orbit. Typical services use digital broadcasting to provide multiple channels to viewers        Sony VGP-BPS13A/B battery .
• Wireless gaming: new gaming consoles allow players to interact and play in the same game regardless of whether they are playing on different consoles. Players can chat, send text messages as well as record sound and send it to their friends. Controllers also use wireless technology        Sony VGP-BPS13B/B battery .
• They do not have any cords but they can send the information from what is being pressed on the controller to the main console which then processes this information and makes it happen in the game. All of these steps are completed in milliseconds       Sony VGP-BPL9 battery .

Wireless networks

Wireless networking (i.e. the various types of unlicensed 2.4 GHz WiFi devices) is used to meet many needs. Perhaps the most common use is to connect laptop users who travel from location to location   Sony VGP-BPS13B/B battery .

Another common use is for mobile networks that connect via satellite. A wireless transmission method is a logical choice to network a LAN segment that must frequently change locations. The following situations justify the use of wireless technology   Sony VGP-BPL15 battery :

• To span a distance beyond the capabilities of typical cabling,
• To provide a backup communications link in case of normal network failure,
• To link portable or temporary workstations        Dell Inspiron E1505 battery ,
• To overcome situations where normal cabling is difficult or financially impractical, or
• To remotely connect mobile users or networks.

Modes

• radio frequency communication      Dell Latitude E6400 battery ,
• microwave communication, for example long-range line-of-sight via highly directional antennas, or short-range communication, or
• infrared (IR) short-range communication, for example from remote controls or via Infrared Data Association (IrDA).

Applications may involve point-to-point communication, point-to-multipoint communication, broadcasting, cellular networks and other wireless networks   HP Pavilion dv6000 Battery .

Cordless

The term "wireless" should not be confused with the term "cordless", which is generally used to refer to powered electrical or electronic devices that are able to operate from a portable power source (e.g. a battery pack) without any cable or cord to limit the mobility of the cordless device through a connection to the mains power supply  SONY VAIO VGN-FZ Battery .

Some cordless devices, such as cordless telephones, are also wireless in the sense that information is transferred from the cordless telephone to the telephone's base unit via some type of wirelesscommunications link. This has caused some disparity in the usage of the term "cordless", for example in Digital Enhanced Cordless Telecommunications   SONY VAIO VGN-FZ18 Battery .

History

Photophone

The world's first, wireless telephone conversation occurred in 1880, when Alexander Graham Bell and Charles Sumner Tainter invented and patented the photophone, a telephone that conducted audio conversations wirelessly over modulated light beams (which are narrow projections of electromagnetic waves)  SONY VAIO VGN-FZ21E Battery .

In that distant era when utilities did not yet exist to provide electricity, and lasers had not even been conceived of in science fiction, there were no practical applications for their invention, which was highly limited by the availability of both sunlight and good weather       SONY VAIO VGN-FW21E Battery .

Similar to free space optical communication, the photophone also required a clear line of sight between its transmitter and its receiver. It would be several decades before the photophone's principles found their first practical applications in military communications and later in fiber-optic communications  SONY VAIO VGN-NR11S/S Battery .

Early wireless work

David E. Hughes, eight years before Hertz's experiments, transmitted radio signals over a few hundred yards by means of a clockwork keyed transmitter      SONY VAIO VGN-NR11M/S Battery .

As this was before Maxwell's work was understood, Hughes' contemporaries dismissed his achievement as mere "Induction". In 1885, T. A. Edison used a vibrator magnet for induction transmission. In 1888, Edison deployed a system of signaling on the Lehigh Valley Railroad        SONY VAIO VGN-NR11Z/S Battery .

In 1891, Edison obtained the wireless patent for this method using inductance (U.S. Patent 465,971).

In the history of wireless technology, the demonstration of the theory of electromagnetic waves by Heinrich Hertz in 1888 was important       SONY VAIO VGN-NR11Z/T Battery .

The theory of electromagnetic waves was predicted from the research of James Clerk Maxwell and Michael Faraday. Hertz demonstrated that electromagnetic waves could be transmitted and caused to travel through space at straight lines and that they were able to be received by an experimental apparatus        Sony VAIO VGN-FZ21E Battery .

The experiments were not followed up by Hertz. Jagadish Chandra Bose around this time developed an early wireless detection device and helped increase the knowledge of millimeter length electromagnetic waves.Practical applications of wireless radio communication and radio remote control technology were implemented by later inventors, such as Nikola Tesla  Sony VAIO VGN-FW21E Battery .

Radio

The term "wireless" came into public use to refer to a radio receiver or transceiver (a dual purpose receiver and transmitter device), establishing its usage in the field of wireless telegraphy early on; now the term is used to describe modern wireless connections such as in cellular networks and wireless broadband Internet  Sony VAIO VGN-NR11S/S Battery .

It is also used in a general sense to refer to any type of operation that is implemented without the use of wires, such as "wireless remote control" or "wireless energy transfer", regardless of the specific technology (e.g. radio, infrared, ultrasonic) used. Guglielmo Marconi andKarl Ferdinand Braun were awarded the 1909 Nobel Prize for Physics for their contribution to wireless telegraphy  Sony VAIO VGN-NR11Z/S Battery .

The electromagnetic spectrum

Light, colors, AM and FM radio, and electronic devices make use of the electromagnetic spectrum. In the US, the frequencies that are available for use for communication are treated as a public resource and are regulated by the Federal Communications Commission  Sony VAIO VGN-NR11M/S Battery .

This determines which frequency ranges can be used for what purpose and by whom. In the absence of such control or alternative arrangements such as a privatized electromagnetic spectrum, chaos might result if, for example, airlines didn't have specific frequencies to work under and an amateur radio operator were interfering with the pilot's ability to land an airplane  Sony VAIO VGN-NR11Z/T Battery .

Wireless communication spans the spectrum from 9 kHz to 300 GHz. (Also see Spectrum management)

Applications of wireless technology

Security systems

Wireless technology may supplement or replace hard wired implementations in security systems for homes or office buildings  SONY VAIO VGN-FZ180E Battery .

Cellular telephone (phones and modems)

Perhaps the best known example of wireless technology is the cellular telephone and modems. These instruments use radio waves to enable the operator to make phone calls from many locations worldwide       SONY VAIO VGN-FZ220E Battery .

They can be used anywhere that there is a cellular telephone site to house the equipment that is required to transmit and receive the signal that is used to transfer both voice and data to and from these instruments.

Wi-Fi

Wi-Fi is a wireless local area network that enables portable computing devices to connect easily to the Internet  SONY VAIO VGN-FZ340E Battery .

Standardized as IEEE 802.11 a,b,g,n, Wi-Fi approaches speeds of some types of wiredEthernet. Wi-Fi hot spots have been popular over the past few years. Some businesses charge customers a monthly fee for service, while others have begun offering it for free in an effort to increase the sales of their goods      SONY VAIO VGN-FZ430E Battery .

Wireless energy transfer

Wireless energy transfer is a process whereby electrical energy is transmitted from a power source to an electrical load that does not have a built-in power source, without the use of interconnecting wires        SONY VAIO VGN-FZ460E Battery .

Computer interface devices

Answering the call of customers frustrated with cord clutter, many manufactures of computer peripherals turned to wireless technology to satisfy their consumer base          SONY VAIO VGN-FZ480E Battery .

Originally these units used bulky, highly limited transceivers to mediate between a computer and a keyboard and mouse, however more recent generations have used small, high quality devices, some even incorporating Bluetooth. These systems have become so ubiquitous that some users have begun complaining about a lack of wired peripherals   SONY VAIO VGN-FZ4000 Battery .

Wireless devices tend to have a slightly slower response time than their wired counterparts, however the gap is decreasing. Initial concerns about the security of wireless keyboards have also been addressed with the maturation of the technology   SONY VAIO VGN-FZ31E Battery .

In computer networking, a wireless access point (WAP) is a device that allows wireless devices to connect to a wired network using Wi-Fi, Bluetooth or related standards. The WAP usually connects to a router (via a wired network), and can relay data between the wireless devices (such as computers or printers) and wired devices on the network   SONY VAIO VGN-FZ31B Battery .

Industrial grade WAPs are rugged, with a metal cover and a DIN rail mount. During operations they can tolerate a wider temperature range, high humidity and exposure to water, dust, and oil. Wireless security includes: WPA-PSK, WPA2, IEEE 802.1x/RADIUS, WDS, WEP, TKIP, and CCMP (AES) encryption    SONY VAIO VGN-FZ31J Battery .

Unlike home consumer models, industrial wireless access points can also be used as a bridge, router, or a client.

Introduction

Prior to wireless networks, setting up a computer network in a business, home, or school often required running many cables through walls and ceilings in order to deliver network access to all of the network-enabled devices in the building   SONY VAIO VGN-FZ31M Battery .

With the advent of the Wireless Access Point, network users are now able to add devices that access the network with few or no cables. Today's WAPs are built to support a standard for sending and receiving data using radio frequencies rather than cabling. Those standards, and the frequencies they use are defined by the IEEE       SONY VAIO VGN-FZ31Z Battery .

Most WAPs use IEEE 802.11 standards.

Common WAP Applications

A typical corporate use involves attaching several WAPs to a wired network and then providing wireless access to the office LAN. The wireless access points are managed by a WLAN Controller which handles automatic adjustments to RF power, channels, authentication, and security      SONY VAIO VGN-FZ38M Battery .

Further, controllers can be combined to form a wireless mobility group to allow inter-controller roaming. The controllers can be part of a mobility domain to allow clients access throughout large or regional office locations. This saves the clients time and administrators overhead because it can automatically re-associate or re-authenticate        SONY VGP-BPS8 Battery .

A Hot Spot is a common public application of WAPs, where wireless clients can connect to the Internet without regard for the particular networks to which they have attached for the moment. The concept has become common in large cities, where a combination of coffeehouses       SONY VGP-BPS13 Battery ,

libraries, as well as privately owned open access points, allow clients to stay more or less continuously connected to the Internet, while moving around. A collection of connected Hot Spots can be referred to as a lily-pad network.

The majority of WAPs are used in Home wireless networks SONY VGP-BPS13/S Battery .

Home networks generally have only one WAP to connect all the computers in a home. Most are wireless routers, meaning converged devices that include the WAP, a router, and, often, an ethernet switch. Many also include a broadband modem   SONY VGP-BPS13A/B Battery .

In places where most homes have their own WAP within range of the neighbors' WAP, it's possible for technically savvy people to turn off their encryption and set up a wireless community network, creating an intra-city communication network without the need of wired networks       SONY VGP-BPS13B/B Battery .

A WAP may also act as the network's arbitrator, negotiating when each nearby client device can transmit. However, the vast majority of currently installedIEEE 802.11 networks do not implement this, using a distributed pseudo-random algorithm called CSMA/CA instead       SONY VGP-BPS13A/S Battery .

Wireless Access Point vs. Ad Hoc Network

Some people confuse Wireless Access Points with Wireless Ad Hoc networks. An Ad Hoc network uses a connection between two or more devices without using a wireless access point: the devices communicate directly when in range    SONY VGP-BPS13AS Battery.

An Ad Hoc network is used in situations such as a quick data exchange or a multiplayer LAN game because setup is easy and does not require an access point. Due to its peer-to-peer layout, Ad Hoc connections are similar to Bluetooth ones and are generally not recommended for a permanent installation    Dell Inspiron 1320n Battery .

Internet access via Ad Hoc networks, using features like Windows' Internet Connection Sharing, may work well with a small number of devices that are close to each other, but Ad Hoc networks don't scale well. Internet traffic will converge to the nodes with direct internet connection, potentially congesting these nodes      Dell Inspiron 1464 Battery .

For internet-enabled nodes, Access Points have a clear advantage, with the possibility of having multiple access points connected by a wired LAN.

Limitations

One IEEE 802.11 WAP can typically communicate with 30 client systems located within a radius of 100 m    Dell Inspiron 1564 Battery .

However, the actual range of communication can vary significantly, depending on such variables as indoor or outdoor placement, height above ground, nearby obstructions, other electronic devices that might actively interfere with the signal by broadcasting on the same frequency, type of antenna, the current weather, operating radio frequency, and the power output of devices  Dell Inspiron 1764 Battery .

Network designers can extend the range of WAPs through the use of repeaters and reflectors, which can bounce or amplify radio signals that ordinarily would go un-received. In experimental conditions, wireless networking has operated over distances of several hundred kilometers     Dell Studio 1450 Battery .

Most jurisdictions have only a limited number of frequencies legally available for use by wireless networks. Usually, adjacent WAPs will use different frequencies (Channels) to communicate with their clients in order to avoid interference between the two nearby systems      Dell Studio 1457 Battery .

Wireless devices can "listen" for data traffic on other frequencies, and can rapidly switch from one frequency to another to achieve better reception. However, the limited number of frequencies becomes problematic in crowded downtown areas with tall buildings using multiple WAPs       Dell Latitude D610 Battery .

In such an environment, signal overlap becomes an issue causing interference, which results in signal droppage and data errors.

Wireless networking lags behind wired networking in terms of increasing bandwidth and throughput   Toshiba NB100 Battery .

While (as of 2010) typical wireless devices for the consumer market can reach speeds of 300 Mbit/s (megabits per second) (IEEE 802.11n) or 54 Mbit/s (IEEE 802.11g), wired hardware of similar cost reaches 1000 Mbit/s (Gigabit Ethernet). One impediment to increasing the speed of wireless communications comes from Wi-Fi's use of a shared communications medium  Toshiba Satellite M65 battery ,

so a WAP is only able to use somewhat less than half the actual over-the-air rate for data throughput. Thus a typical 54 MBit/s wireless connection actually carries TCP/IP data at 20 to 25 Mbit/s. Users of legacy wired networks expect faster speeds, and people using wireless connections keenly want to see the wireless networks catch up  Toshiba Satellite M60 battery .

By 2008 draft 802.11n based access points and client devices have already taken a fair share of the market place but with inherent problems integrating products from different vendors.

Security

Wireless access has special security considerations        Dell Latitude D830 Battery .

Many wired networks base the security on physical access control, trusting all the users on the local network, but if wireless access points are connected to the network, anyone on the street or in the neighboring office could connect.

The most common solution is wireless traffic encryption. Modern access points come with built-in encryption   Dell Latitude D620 Battery .

The first generation encryption scheme WEP proved easy to crack; the second and third generation schemes, WPA and WPA2, are considered secure if a strong enough password or passphrase is used.

Some WAPs support hotspot style authentication using RADIUS and other authentication servers  Dell Inspiron Mini 10 Battery .

A wireless local area network (WLAN) links two or more devices using some wireless distribution method (typically spread-spectrum or OFDM radio), and usually providing a connection through an access point to the wider internet. This gives users the mobility to move around within a local coverage area and still be connected to the network  Sony VGN-FW11S Battery .

Wireless LANs have become popular in the home due to ease of installation, and the increasing popularity of laptop computers. Public businesses such as coffee shops and malls have begun to offer wireless access to their customers; often for free. Large wireless network projects are being put up in many major cities       Sony VGN-FW11M Battery :

New York City, for instance, has begun a pilot program to cover all five boroughs of the city with wireless Internet access.

In 1970 Norman Abramson, a professor at the University of Hawaii, developed the world’s first wireless computer communication network, ALOHAnet, using low-cost ham-like radios        Sony VGN-FW139E/H battery .

The system included seven computers deployed over four islands to communicate with the central computer on the Oahu Island without using phone lines.

"In 1979, F.R. Gfeller and U. Bapst published a paper in the IEEE Proceedings reporting an experimental wireless local area network using diffused infrared communications         Dell Latitude E5400 Battery .

Shortly thereafter, in 1980, P. Ferrert reported on an experimental application of a single code spread spectrumradio for wireless terminal communications in the IEEE National Telecommunications Conference. In 1984, a comparison between infrared and CDMA spread spectrum communications for wireless office information networks was published by Kaveh Pahlavan in IEEE Computer Networking Symposium which appeared later in the IEEE Communication Society Magazine       Dell Latitude E4200 Battery .

In May 1985, the efforts of Marcus led the FCC to announce experimental ISM bands for commercial application of spread spectrum technology. Later on, M. Kavehrad reported on an experimental wireless PBX system using code division multiple access      Dell Inspiron 300M Battery .

These efforts prompted significant industrial activities in the development of a new generation of wireless local area networks and it updated several old discussions in the portable and mobile radio industry.

The first generation of wireless data modems was developed in the early 1980s by amateur radio operators, who commonly referred to this as packet radio        Dell Vostro A840 Battery .

They added a voice band data communication modem, with data rates below 9600-bit/s, to an existing short distance radio system, typically in the two meter amateur band. The second generation of wireless modems was developed immediately after the FCC announcement in the experimental bands for non-military use of the spread spectrum technology   Dell Studio 1737 battery .

These modems provided data rates on the order of hundreds of kbit/s. The third generation of wireless modem then aimed at compatibility with the existing LANs with data rates on the order of Mbit/s. Several companies developed the third generation products with data rates above 1 Mbit/s and a couple of products had already been announced by the time of the first IEEE Workshop on Wireless LANs       Dell Inspiron E1505 battery ."

"The first of the IEEE Workshops on Wireless LAN was held in 1991. At that time early wireless LAN products had just appeared in the market and the IEEE 802.11 committee had just started its activities to develop a standard for wireless LANs. The focus of that first workshop was evaluation of the alternative technologies          Dell RM791 battery .

By 1996, the technology was relatively mature, a variety of applications had been identified and addressed and technologies that enable these applications were well understood. Chip sets aimed at wireless LAN implementations and applications, a key enabling technology for rapid market growth, were emerging in the market      Dell XPS M1530 battery .

Wireless LANs were being used in hospitals, stock exchanges, and other in building and campus settings for nomadic access, point-to-point LAN bridges, ad-hoc networking, and even larger applications through internetworking. The IEEE 802.11 standard and variants and alternatives      Dell XPS M2010 battery ,

such as the wireless LAN interoperability forum and the European HiperLAN specification had made rapid progress, and the unlicensed PCS Unlicensed Personal Communications Services and the proposed SUPERNet, later on renamed as U-NII, bands also presented new opportunities       Acer Aspire One battery ."

WLAN hardware was initially so expensive that it was only used as an alternative to cabled LAN in places where cabling was difficult or impossible. Early development included industry-specific solutions and proprietary protocols, but at the end of the 1990s these were replaced by standards          Toshiba Satellite P10 Battery ,

primarily the various versions of IEEE 802.11 (commonly misunderstood as equal to trademark Wi-Fi of Wi-Fi_Alliance). An alternative ATM-like 5 GHz standardized technology, HiperLAN/2, has so far not succeeded in the market, and with the release of the faster 54 Mbit/s 802.11a (5 GHz) and 802.11g (2.4 GHz) standards, almost certainly never will   SONY VGN-FZ210CE Battery .

Stations

All components that can connect into a wireless medium in a network are referred to as stations.

All stations are equipped with wireless network interface cards (WNICs).

Wireless stations fall into one of two categories: access points, and clients          Dell Precision M70 Battery .

Access points (APs), normally routers, are base stations for the wireless network. They transmit and receive radio frequencies for wireless enabled devices to communicate with.

Wireless clients can be mobile devices such as laptops, personal digital assistants, IP phones and other smartphones, or fixed devices such as desktops and workstations that are equipped with a wireless network interface           Toshiba Satellite L305 Battery .

Basic service set

The basic service set (BSS) is a set of all stations that can communicate with each other.

There are two types of BSS: Independent BSS (also referred to as IBSS), and infrastructure BSS   Toshiba Satellite T4900 Battery .

Every BSS has an identification (ID) called the BSSID, which is the MAC address of the access point servicing the BSS.

An independent BSS (IBSS) is an ad-hoc network that contains no access points, which means they can not connect to any other basic service set              Toshiba PA3399U-2BRS battery .

An infrastructure can communicate with other stations not in the same basic service set by communicating through access points.

Extended service set

An extended service set (ESS) is a set of connected BSSes. Access points in an ESS are connected by a distribution system. Each ESS has an ID called the SSID which is a 32-byte (maximum) character string         Toshiba Satellite A200 Battery .

Distribution system

A distribution system (DS) connects access points in an extended service set. The concept of a DS can be used to increase network coverage through roaming between cells           Toshiba Satellite 1200 Battery .

DS can be wired or wireless. Current wireless distribution systems are mostly based on WDS or MESH protocols, though other systems are in use, too.

Peer-to-peer

Peer-to-Peer or ad-hoc wireless LAN

An ad-hoc network is a network where stations communicate only peer to peer (P2P)          Toshiba Satellite M300 Battery .

There is no base and no one gives permission to talk. This is accomplished using the Independent Basic Service Set (IBSS).

A peer-to-peer (P2P) network allows wireless devices to directly communicate with each other. Wireless devices within range of each other can discover and communicate directly without involving central access points  SONY VGP-BPS13A/Q Battery .

This method is typically used by two computers so that they can connect to each other to form a network.

If a signal strength meter is used in this situation, it may not read the strength accurately and can be misleading, because it registers the strength of the strongest signal, which may be the closest computer        SONY VGP-BPS13A/Q Battery .

IEEE 802.11 define the physical layer (PHY) and MAC (Media Access Control) layers based on CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance). The 802.11 specification includes provisions designed to minimize collisions, because two mobile units may both be in range of a common access point, but out of range of each other        SONY VGP-BPS13B/Q Battery .

The 802.11 has two basic modes of operation: Ad hoc mode enables peer-to-peer transmission between mobile units. Infrastructure mode in which mobile units communicate through an access point that serves as a bridge to a wired network infrastructure is the more common wireless LAN application the one being covered       SONY VGP-BPS13B/Q Battery .

Since wireless communication uses a more open medium for communication in comparison to wired LANs, the 802.11 designers also included shared-key encryption mechanisms: Wired Equivalent Privacy (WEP), Wi-Fi Protected Access (WPA, WPA2), to secure wireless computer networks        SONY VGP-BPS13/Q Battery .

Bridge

A bridge can be used to connect networks, typically of different types. A wireless Ethernet bridge allows the connection of devices on a wired Ethernet network to a wireless network. The bridge acts as the connection point to the Wireless LAN       SONY VGP-BPS13/Q Battery .

Wireless distribution system

A Wireless Distribution System is a system that enables the wireless interconnection of access points in an IEEE 802.11 network. It allows a wireless network to be expanded using multiple access points without the need for a wired backbone to link them, as is traditionally required            SONY VGP-BPS21A/B Battery .

The notable advantage of WDS over other solutions is that it preserves the MAC addresses of client packets across links between access points.

An access point can be either a main, relay or remote base station. A main base station is typically connected to the wired Ethernet  SONY VGP-BPS21/S Battery .

A relay base station relays data between remote base stations, wireless clients or other relay stations to either a main or another relay base station. A remote base station accepts connections from wireless clients and passes them to relay or main stations. Connections between "clients" are made using MAC addresses rather than by specifying IP assignments  SONY VGP-BPS21B Battery .

All base stations in a Wireless Distribution System must be configured to use the same radio channel, and share WEP keys or WPA keys if they are used. They can be configured to different service set identifiers. WDS also requires that every base station be configured to forward to others in the system       SONY VGP-BPS21A Battery .

WDS may also be referred to as repeater mode because it appears to bridge and accept wireless clients at the same time (unlike traditional bridging). It should be noted, however, that throughput in this method is halved for all clients connected wirelessly  SONY VGP-BPS21 Battery .

When it is difficult to connect all of the access points in a network by wires, it is also possible to put up access points as repeaters.

Roaming

There are 2 definitions for wireless LAN roaming:

• Internal Roaming (1): The Mobile Station (MS) moves from one access point (AP) to another AP within a home network because the signal strength is too weak       Sony VGP-BPS21A/B Battery .
• An authentication server (RADIUS) assumes the re-authentication of MS via 802.1x (e.g. with PEAP). The billing of QoS is in the home network. A Mobile Station roaming from one access point to another often interrupts the flow of data between the Mobile Station and an application connected to the network   Sony VGP-BPS21/S Battery .
• The Mobile Station, for instance, periodically monitors the presence of alternative access points (ones that will provide a better connection). At some point, based upon proprietary mechanisms, the Mobile Station decides to re-associate with an access point having a stronger wireless signal         Sony VGP-BPS21B Battery .
• The Mobile Station, however, may lose a connection with an access point before associating with another access point. In order to provide reliable connections with applications, the Mobile Station must generally include software that provides session persistence       Sony VGP-BPS21A Battery .

• External Roaming (2): The MS(client) moves into a WLAN of another Wireless Internet Service Provider (WISP) and takes their services (Hotspot). The user can independently of his home network use another foreign network, if this is open for visitors. There must be special authentication and billing systems for mobile services in a foreign network  Sony VGP-BPS21 Battery .

Wireless network refers to any type of computer network that is not connected by cables of any kind. It is a method by which telecommunications networks and enterpise (business), installations avoid the costly process of introducing cables into to a building, or as a connection between various equipment locations   Sony Vaio PCG-5G2L Battery .

Wireless telecommunications networks are generally implemented and administered using a transmission system called radio waves. This implementation takes place at the physical level, (layer), of the network structure.

Wireless PAN

Wireless Personal Area Networks (WPANs) interconnect devices within a relatively small area, generally within a persons reach  Sony Vaio PCG-5G3L Battery .

For example, both Bluetooth radio and invisible Infrared light provides a WPAN for interconnecting a headset to a laptop. ZigBee also supports WPAN applications. Wi-Fi PANs are becoming commonplace (2010) as equipment designers start to integrate Wi-Fi into a variety of consumer electronic devices      Sony Vaio PCG-5J1L Battery .

Intel "My WiFi" and Windows 7 "virtual Wi-Fi" capabilities have made Wi-Fi PANs simpler and easier to set up and configure.

Wireless LAN

A wireless local area network (WLAN) links two or more devices using a wireless distribution method, providing a connection through an access point to the wider internet      Sony Vaio PCG-5K2L Battery .

The use of spread-spectrumor OFDM technologies also gives users the mobility to move around within a local coverage area, and still remain connected to the network.

• Wi-Fi: "Wi-Fi" is a term used to describe 802.11 WLANs, although it is technically a declared standard of interoperability between 802.11 devices      Sony Vaio PCG-5J2L Battery .
• Fixed Wireless Data: This implements point to point links between computers or networks at two distant locations, often using dedicated microwave or modulated laser light beams over line of sightpaths. It is often used in cities to connect networks in two or more buildings without installing a wired link   Sony Vaio PCG-5K1L Battery .

Wireless MAN

Wireless Metropolitan Area Networks are a type of wireless network that connects several Wireless LANs.

• WiMAX is a type of Wireless MAN and is described by the IEEE 802.16 standard        Sony Vaio PCG-5L1L Battery .

Wireless WAN

wireless wide area networks are wireless networks that typically cover large outdoor areas. These networks can be used to connect branch offices of business or as a public internet access system         Sony Vaio PCG-6S2L Battery .

They are usually deployed on the 2.4 GHz band. A typical system contains base station gateways, access points and wireless bridging relays. Other configurations are mesh systems where each access point acts as a relay also. When combined with renewable energy systems such as photo-voltaic solar panels or wind systems they can be stand alone systems       Sony Vaio PCG-6S3L Battery .

Mobile devices networks

With the development of smart phones, cellular telephone networks routinely carry data in addition to telephone conversations:

• Global System for Mobile Communications (GSM): The GSM network is divided into three major systems: the switching system, the base station system, and the operation and support system      Sony Vaio PCG-6V1L Battery .
• The cell phone connects to the base system station which then connects to the operation and support station; it then connects to the switching station where the call is transferred to where it needs to go. GSM is the most common standard and is used for a majority of cell phones      Sony Vaio PCG-6W1L Battery .
• Personal Communications Service (PCS): PCS is a radio band that can be used by mobile phones in North America and South Asia. Sprint happened to be the first service to set up a PCS.
• D-AMPS: Digital Advanced Mobile Phone Service, an upgraded version of AMPS, is being phased out due to advancement in technology. The newer GSM networks are replacing the older system           Sony Vaio PCG-6W2L Battery .

Uses

An embedded RouterBoard 112 withU.FL-RSMA pigtail and R52 mini PCI Wi-Ficard widely used by wireless Internetservice providers (WISPs) in the Czech Republic        Sony Vaio PCG-6W3L Battery .

Wireless networks continue to develop, usage has grown in 2010. Cellular phones are part of everyday wireless networks, allowing easy personal communications. Inter-continental network systems use radio satellites to communicate across the world. Emergency services such as the police utilize wireless networks to communicate effectively      Sony Vaio PCG-7111L Battery .

Individauls and businesses use wireless networks to send and share data rapidly, whether it be in a small office building or across the world.

Another use for wireless networks is a cost effective means to connect to the Internet, in regions where the telecommunications infrastructure is both poor and lacking in resources, typically in rural areas and developing countries  Sony Vaio PCG-7112L Battery .

Compatibility issues also arise when dealing with wireless networks. Different devices may have compatibility issues, or might require modifications to solve these issues. Wireless networks are often typically slower than those found in modern versions of Ethernet cable connected installations     Sony Vaio PCG-7113L Battery .

A wireless network is more vulnerable, because anyone can intercept and sometimes divert a network broadcasting signal when point to point connections are used. Many wirless networks use WEP - Wired Equivalent Privacy - security systems. These have been found to be still vulnerable to intrusion      Sony Vaio PCG-7133L Battery .

Though WEP does block some intruders, the security problems have caused some businesses to continue using wired networks until a more suitable security system can be introduced. The use of suitable firewalls overcome some security problems in wireless networks that are vulnerable to attempted unauthorised access    Sony Vaio PCG-7Z2L Battery .

Environmental concerns and health hazard

Starting around 2009, there have been increased concerns about the safety of wireless communications, despite little evidence of health risks so far      Sony Vaio PCG-8Y1L Battery .

The president of Lakehead University refused to agree to installation of a wireless network citing a California Public Utilities Commission study which said that the possible risk of tumors and other diseases due to exposure to electromagnetic fields (EMFs) needs to be further investigated        Sony Vaio PCG-8Y2L Battery .

Wireless community networks or wireless community projects are the organizations that attempt to take a grassroots approach to providing a viable alternative to municipal wireless networks for consumers.

Because of evolving technology and locales, there are at least four different types of solution  Sony Vaio PCG-8Z1L Battery :

• Cluster: Advocacy groups which simply encourage sharing of unmetered internet bandwidth via Wi-Fi, may also index nodes, suggest uniform SSID (for low-quality roaming), supply equipment, dns services, etc.
• Mesh: Technology groups which coordinate building a mesh network to provide Wi-Fi access to the internet   Sony Vaio PCG-8Z2L Battery
• WISP: A mesh that forwards all traffic back to consolidated link aggregation point(s) that have centralized access to the internet
• WUG: A wireless user group run by wireless enthusiasts. An open network not used for the reselling of internet. Running a combination of various off the shelf WIFI hardware running in the license free ISM bands 2.4 GHz/5.8 GHz Sony VAIO PCG-5G2L Battery

Certain countries regulate the selling of internet access, requiring a license to sell internet access over a wireless network. In South Africa it is regulated byICASA .They require that WISP's apply for a VANS or ECNS/ECS license before being allowed to resell internet access over a wireless link            Sony VAIO PCG-5G3L Battery .

The cluster and mesh approaches are more common but rely primarily on the sharing of unmetered residential and business DSL and cable Internet. This sort of usage might be non-compliant with the Terms of Service (ToS) of the typical local providers that deliver their service via the consumer phone and cable duopoly       Sony VAIO PCG-5J1L Battery .

Wireless community network sometimes advocate complete freedom from censorship, and this position may be at odds with the Acceptable Use Policies of some commercial services used. Some ISPs do allow sharing or reselling of bandwidth       Sony VAIO PCG-5K2L Battery .

History

These projects are in many senses an evolution of amateur radio, and more specifically packet radio, as well as an outgrowth of the free software community (which in itself substantially overlaps with amateur radio) Sony VAIO PCG-5J2L Battery .

The key to using standard wireless networking devices designed for short-range use for multi-kilometre Long Range Wi-Fi linkups is the use of high-gain directional antennas. Rather than purchasing commercially available units, such groups sometimes advocate homebuilt antenna construction          Sony VAIO PCG-5K1L Battery .

Examples include the cantenna, which is typically constructed from aPringles potato chip can, and RONJA, an optical link that can be made from a smoke flue and LEDs, with circuitry and instructions released under the GFDL. As with other wireless mesh networks, three distinct generations of mesh networks are used in wireless community networks      Sony VAIO PCG-5L1L Battery .

In particular, in the 2004 timeframe, some mesh projects suffered poor performance when scaled up.

Organization

Organizationally, a wireless community network requires either a set of affordable commercial technical solutions or a critical mass of hobbyists willing to tinker to maintain operations        Sony VAIO PCG-6S2L Battery .

Mesh networks require that a high level of community participation and commitment be maintained for the network to be viable. The mesh approach currently requires uniform equipment. One market-driven aspect of the mesh approach is that users who receive a weak mesh signal can often convert it to a strong signal by obtaining and operating a repeater node, thus extending the mesh networkSony VAIO PCG-6S3L Battery .

Such volunteer organizations focusing in technology that is rapidly advancing sometimes have schisms and mergers. The Wi-Fi service provided by such groups is usually free and without the stigma ofpiggybacking (internet access). An alternative to the voluntary model is to use a co-operative structure     Sony VAIO PCG-6V1L Battery .

One issue with corporate wireless networks in general, and WLANs in particular, involves the need for security. Many early access points could not discern whether or not a particular user had authorization to access the network    Sony VAIO PCG-6W1L Battery .

Although this problem reflects issues that have long troubled many types of wired networks (it has been possible in the past for individuals to plug computers into randomly available Ethernet jacks and get access to a local network), this did not usually pose a significant problem, since many organizations had reasonably good physical security   Sony VAIO PCG-6W2L Battery .

However, the fact that radio signals bleed outside of buildings and across property lines makes physical security largely irrelevant to Piggybackers. Such corporate issues are covered in wireless security         Sony VAIO PCG-6W3L Battery .

Concerns

Anyone within the geographical network range of an open, unencrypted wireless network can 'sniff' or record the traffic, gain unauthorized access to internal network resources as well as to the internet, and then possibly send spam or do other illegal actions using the wireless network's IP address, all of which are rare for home routers but may be significant concerns for office networksSony VAIO PCG-7111L Battery .

If router security is not activated or if the owner deactivates it for convenience, it creates a free hotspot. Since most 21st century laptop PCs have wireless networking built in (cf. Intel 'Centrino' technology), they don't need a third-party adapter such as a PCMCIA Card or USB dongle     Sony VAIO PCG-7112L Battery .

Built in wireless networking might be enabled by default, without the owner realizing it, thus broadcasting the laptop's accessibility to any computer nearby.

Modern operating systems such as Mac OS, or Microsoft Windows make it fairly easy to set up a PC as a wireless LAN 'base station' using Internet Connection Sharing, thus allowing all the PCs in the home to access the Internet via the 'base' PC Sony VAIO PCG-7113L Battery .

However, lack of knowledge about the security issues in setting up such systems often means that someone nearby may also use the connection. Such "piggybacking" is usually achieved without the wireless network operators knowledge; it may even be without the knowledge of the intruding user if their computer automatically selects a nearby unsecured wireless network to use as an access point   Sony VAIO PCG-7133L Battery .

Security options

There are three principal ways to secure a wireless network.

• For closed networks (like home users and organizations) the most common way is to configure access restrictions in the access points. Those restrictions may include encryption and checks onMAC address           Sony VAIO PCG-7Z1L Battery .
• Another option is to disable ESSID broadcasting, making the access point difficult for outsiders to detect. Wireless Intrusion Prevention Systems can be used to provide wireless LAN security in this network model    Sony VAIO PCG-7Z2L Battery .
• For commercial providers, hotspots, and large organizations, the preferred solution is often to have an open and unencrypted, but completely isolated wireless network. The users will at first have no access to the Internet nor to any local network resources           Sony VAIO PCG-8Y1L Battery .
• Commercial providers usually forward all web traffic to a captive portal which provides for payment and/or authorization. Another solution is to require the users to connect securely to a privileged network using VPN.
• Wireless networks are less secure than wired ones        Sony VAIO PCG-8Y2L Battery .
• in many offices intruders can easily visit and hook up their own computer to the wired network without problems, gaining access to the network, and it's also often possible for remote intruders to gain access to the network through backdoors like Back Orifice       Sony VAIO PCG-8Z1L Battery .
• One general solution may be end-to-end encryption, with independent authentication on all resources that shouldn't be available to the public.

Access Control at the Access Point level

One of the simplest techniques is to only allow access from known, approved MAC addresses   Sony VAIO PCG-8Z2L Battery .

However, this approach gives no security against sniffing, and client devices can easily spoof MAC addresses, leading to the need for more advanced security measures.

Some access points can also support "AP isolation" which isolates all wireless clients and wireless devices on the network from each other   WD passport essential (500GB/640GB) .

Wireless devices will be able to communicate with the gateway but not with each other in the network.

Another very simple technique is to have a secret ESSID (id/name of the wireless network), though anyone who studies the method will be able to sniff the ESSID      WD passport essential (250GB/320GB) .

Today all (or almost all) access points incorporate Wired Equivalent Privacy (WEP) encryption and most wireless routers are sold with WEP turned on. However, security analysts have criticized WEP's inadequacies, and the U.S. FBI has demonstrated the ability to break WEP protection in only three minutes using tools available to the general public (see aircrack)  WD  passport essential SE (750GB/1TB)   .

The Wi-Fi Protected Access (WPA and WPA2) security protocols were later created to address these problems. If a weak password, such as a dictionary word or short character string is used, WPA and WPA2 can be cracked. Using a long enough random password (e.g. 14 random letters) or passphrase (e.g. 5 randomly chosen words) makes pre-shared key WPA virtually uncrackable  WD  passport elite(250GB/320GB) .

The second generation of the WPA security protocol (WPA2) is based on the final IEEE 802.11i amendment to the 802.11 standard and is eligible for FIPS 140-2 compliance. With all those encryption schemes, any client in the network that knows the keys can read all the traffic       WD passport elite(500GB/640GB) .

Restricted access networks

Solutions include a newer system for authentication, IEEE 802.1x, that promises to enhance security on both wired and wireless networks. Wireless access points that incorporate technologies like these often also have routers built in, thus becoming wireless gateways      WD  passport studio for Mac(320GB/500GB) .

End-to-End encryption

One can argue that both layer 2 and layer 3 encryption methods are not good enough for protecting valuable data like passwords and personal emails. Those technologies add encryption only to parts of the communication path, still allowing people to spy on the traffic if they have gained access to the wired network somehow     WD  passport studio for Mac(500GB/640GB) .

The solution may be encryption and authorization in the application layer, using technologies like SSL, SSH, GnuPG, PGP and similar.

The disadvantage with the end to end method is, it may fail to cover all traffic. With encryption on the router level or VPN, a single switch encrypts all traffic, even UDP and DNS lookups         WD  Elements series(250GB/320GB) .

With end-to-end encryption on the other hand, each service to be secured must have its encryption "turned on," and often every connection must also be "turned on" separately. For sending emails, every recipient must support the encryption method, and must exchange keys correctly         WD  Elements SE(500GB/640GB) .

For Web, not all web sites offer https, and even if they do, the browser sends out IP addresses in clear text.

The most prized resource is often access to Internet. An office LAN owner seeking to restrict such access will face the non trivial enforcement task of having each user authenticate himself for the router     WD Elements SE(750GB/1TB) .

Open Access Points

Today, there is almost full wireless network coverage in many urban areas - the infrastructure for the wireless community network (which some consider to be the future of the internet) is already in place        WD  Elements desktop(500GB/640GB) .

One could roam around and always be connected to Internet if the nodes were open to the public, but due to security concerns, most nodes are encrypted and the users don't know how to disable encryption. Many people consider it proper etiquette to leave access points open to the public, allowing free access to Internet       WD  Elements desktop(750GB/1TB) .

Others think the default encryption provides substantial protection at small inconvenience, against dangers of open access that they fear may be substantial even on a home DSL router.

The density of access points can even be a problem - there are a limited number of channels available, and they partly overlap   WD  Elements desktop(1.5 TB/2TB) .

Each channel can handle multiple networks, but places with many private wireless networks (for example, apartment complexes), the limited number of Wi-Fi radio channels might cause slowness and other problems       WD  passport essential SE (750GB/1TB)--USB 3.0)   .

According to the advocates of Open Access Points, it shouldn't involve any significant risks to open up wireless networks for the public:

• The wireless network is after all confined to a small geographical area         WD  passport essential (500GB/640GB) .
• A computer connected to the Internet and having improper configurations or other security problems can be exploited by anyone from anywhere in the world, while only clients in a small geographical range can exploit an open wireless access point. Thus the exposure is low with an open wireless access point, and the risks with having an open wireless network are small  WD  passport for Mac(320GB/500GB) .
• However, one should be aware that an open wireless router will give access to the local network, often including access to file shares and printers.
• The only way to keep communication truly secure is to use end-to-end encryption     WD  passport for Mac(640GB/1TB) .
• For example, when accessing an internet bank, one would almost always use strong encryption from the web browser and all the way to the bank - thus it shouldn't be risky to do banking over an unencrypted wireless network. The argument is that anyone can sniff the traffic applies to wired networks too         My book essential 4 generation  (640GB/1TB) ,
• where system administrators and possible crackers have access to the links and can read the traffic. Also, anyone knowing the keys for an encrypted wireless network can gain access to the data being transferred over the network   WD  My book essential 4 generation( 1.5TB/2TB) .
• If services like file shares, access to printers etc. are available on the local net, it is advisable to have authentication (i.e. by password) for accessing it (one should never assume that the private network is not accessible from the outside). Correctly set up, it should be safe to allow access to the local network to outsiders   WD  My book elite( 1TB/1.5TB) .
• With the most popular encryption algorithms today, a sniffer will usually be able to compute the network key in a few minutes.
• It is very common to pay a fixed monthly fee for the Internet connection, and not for the traffic - thus extra traffic will not hurtWD  My book studio(1TB/2TB) .
• Where Internet connections are plentiful and cheap, freeloaders will seldom be a prominent nuisance  WD  My book essential 4 generation( 1.5TB/2TB) .

On the other hand, in some countries including Germany, persons providing a n open access point may be made (partially) liable for any illegal activity conducted via this access point. Also, many contracts with ISPs specify that the connection may not be shared with other persons      WD  My book elite(640GB/2TB) .

Autodesk 3ds Max, formerly 3D Studio MAX, is a modeling, animation and rendering package developed by Autodesk Media and Entertainment. It has modeling capabilities, a flexible plugin architecture and is able to be used on the Microsoft Windows platform  (Dell XPS M1210 Battery) http://www.hdd-shop.co.uk .

It's frequently used by video game developers, TV commercial studios and architectural visualization studios. It is also used for movie effects and movie pre-visualization.

In addition to its modeling and animation tools, the latest version of 3ds Max also features shaders   (Dell Studio XPS 1640 Battery)

(such as ambient occlusion and subsurface scattering), dynamic simulation, particle systems, radiosity, normal map creation and rendering, global illumination, a customizable user interface, and its own scripting language   (Dell Vostro 1710 Battery) .

Early history and releases

The original 3D Studio product was created for the DOS platform by the Yost Group and published by Autodesk. After 3D Studio Release 4, the product was rewritten for the Windows NT platform, and re-named "3D Studio MAX." This version was also originally created by the Yost Group  (Dell KM958 battery)      .

It was released by Kinetix, which was at that time Autodesk's division of media and entertainment. Autodesk purchased the product at the second release mark of the 3D Studio MAX version and internalized development entirely over the next two releases  Dell Studio 1555 battery .

Later, the product name was changed to "3ds max" (all lower case) to better comply with the naming conventions of Discreet, a Montreal-based software company which Autodesk had purchased. At release 8, the product was again branded with the Autodesk logo, and the name was again changed to "3ds Max" (upper and lower case)      (Sony VGP-BPS13 battery)    .

At release 2009, the product name changed to "Autodesk 3ds Max".

Features

MAXScript

MAXScript is a built-in scripting language, and can be used to automate repetitive tasks, combine existing functionality in new ways, develop new tools and user interfaces and much more      (Sony VGP-BPS13/B battery)         .

Plugin modules can be created entirely in MAXScript.

Character Studio

Character Studio was a plugin which since version 4 of Max is now integrated in 3D Studio Max, helping user to animate virtual characters   (Sony VGP-BPS13/S battery)        .

The system works using a character rig or "Biped" which is pre-made and allows the user to adjust the rig to fit the character they will be animating . Dedicated curve editors and motion capture data import tools make Character Studio ideal for character animation  (Sony VGP-BPS13A/B battery)      .

"Biped" objects have other useful features that automated the production of walk cycles and movement paths, as well as secondary motion.

Scene Explorer

Scene Explorer, a tool that provides a hierarchical view of scene data and analysis, facilitates working with more complex scenes (Sony VGP-BPS13B/B battery)      .

Scene Explorer has the ability to sort, filter, and search a scene by any object type or property (including metadata). Added in 3ds Max 2008, it was the first component to facilitate .NET managed code in 3ds Max outside of MAXScript.

DWG Import

3ds Max supports both import and linking of DWG files      (Sony VGP-BPL9 battery)         .

Improved memory management in 3ds Max 2008 enables larger scenes to be imported with multiple objects.

Texture Assignment/Editing

3ds Max offers operations for creative texture and planar mapping, including tiling, mirroring, decals, angle, rotate, blur, UV stretching, and relaxation; Remove Distortion; Preserve UV; and UV template image export      (Sony VGP-BPS13B/B battery)    .

The texture workflow includes the ability to combine an unlimited number of textures, a material/map browser with support for drag-and-drop assignment, and hierarchies with thumbnails. UV workflow features include Pelt mapping, which defines custom seams and enables users to unfold UVs according to those seams    Sony VGP-BPL15 battery ;

copy/paste materials, maps and colors; and access to quick mapping types (box, cylindrical, spherical).

General Keyframing

Two keying modes — set key and auto key — offer support for different keyframing workflows  Dell Inspiron E1505 battery .

Fast and intuitive controls for keyframing — including cut, copy, and paste — let the user create animations with ease. Animation trajectories may be viewed and edited directly in the viewport.

Constrained Animation

Objects can be animated along curves with controls for alignment   Dell Latitude E6400 battery ,

banking, velocity, smoothness, and looping, and along surfaces with controls for alignment. Weight path-controlled animation between multiple curves, and animate the weight. Objects can be constrained to animate with other objects in many ways — including look at, orientation in different coordinate spaces, and linking at different points in time   HP Pavilion dv6000 Battery .

These constraints also support animated weighting between more than one target.

All resulting constrained animation can be collapsed into standard keyframes for further editing.

Skinning

Either the Skin or Physique modifier may be used to achieve precise control of skeletal deformation  SONY VAIO VGN-FZ Battery ,

so the character deforms smoothly as joints are moved, even in the most challenging areas, such as shoulders. Skin deformation can be controlled using direct vertex weights, volumes of vertices defined by envelopes, or both.

Capabilities such as weight tables         SONY VAIO VGN-FZ18 Battery ,

paintable weights, and saving and loading of weights offer easy editing and proximity-based transfer between models, providing the accuracy and flexibility needed for complicated characters.

The rigid bind skinning option is useful for animating low-polygon models or as a diagnostic tool for regular skeleton animation  SONY VAIO VGN-FZ21E Battery.

Additional modifiers, such as Skin Wrap and Skin Morph, can be used to drive meshes with other meshes and make targeted weighting adjustments in tricky areas.

Skeletons and Inverse Kinematics (IK)

Characters can be rigged with custom skeletons using 3ds Max bones, IK solvers, and rigging tools  SONY VAIO VGN-FW21E Battery .

All animation tools — including expressions, scripts, list controllers, and wiring — can be used along with a set of utilities specific to bones to build rigs of any structure and with custom controls, so animators see only the UI necessary to get their characters animated   SONY VAIO VGN-NR11S/S Battery .

Four plug-in IK solvers ship with 3ds Max: history-independent solver, history-dependent solver, limb solver, and spline IK solver. These powerful solvers reduce the time it takes to create high-quality character animation. The history-independent solver delivers smooth blending between IK and FK animation and uses preferred angles to give animators more control over the positioning of affected bones  SONY VAIO VGN-NR11M/S Battery .

The history-dependent solver can solve within joint limits and is used for machine-like animation. IK limb is a lightweight two-bone solver, optimized for real-time interactivity, ideal for working with a character arm or leg. Spline IK solver provides a flexible animation system with nodes that can be moved anywhere in 3D space         SONY VAIO VGN-NR11Z/S Battery .

It allows for efficient animation of skeletal chains, such as a character’s spine or tail, and includes easy-to-use twist and roll controls.

Integrated Cloth Solver

In addition to reactor’s cloth modifier, 3ds Max software has an integrated cloth-simulation engine that enables the user to turn almost any 3D object into clothing, or build garments from scratch   SONY VAIO VGN-NR11Z/T Battery .

Collision solving is fast and accurate even in complex simulations.(image.3ds max.jpg)

Local simulation lets artists drape cloth in real time to set up an initial clothing state before setting animation keys.

Cloth simulations can be used in conjunction with other 3ds Max dynamic forces, such as Space Warps  Sony VAIO VGN-FZ21E Battery .

Multiple independent cloth systems can be animated with their own objects and forces. Cloth deformation data can be cached to the hard drive to allow for nondestructive iterations and to improve playback performance         Sony VAIO VGN-FW21E Battery .

Integration with Autodesk Vault

Autodesk Vault plug-in, which ships with 3ds Max, consolidates users’ 3ds Max assets in a single location, enabling them to automatically track files and manage work in progress. Users can easily and safely share, find, and reuse 3ds Max (and design) assets in a large-scale production or visualization environment   Sony VAIO VGN-NR11S/S Battery .

Industry usage

Many recent films have made use of 3ds Max, or previous versions of the program under previous names, in CGI animation, such as Avatar and 2012, which contain computer generated graphics from 3ds Max alongside live-action acting  Sony VAIO VGN-NR11Z/S Battery .

3ds Max has also been used in the development of 3D computer graphics for a number of video games.

Architectural and engineering design firms use 3ds Max for developing conceptual art and previsualization  Sony VAIO VGN-NR11M/S Battery .

Educational usage

Educational programs at secondary and tertiary level use 3ds Max in their courses on 3D computer graphics and computer animation. Students in the FIRST competition for 3d animation are known to use 3ds Max       Sony VAIO VGN-NR11Z/T Battery .

Modeling techniques

Polygon modeling

Polygon modeling is more common with game design than any other modeling technique as the very specific control over individual polygons allows for extreme optimization   SONY VAIO VGN-FZ180E Battery .

Usually, the modeler begins with one of the 3ds max primitives, and using such tools as bevel and extrude, adds detail to and refines the model. Versions 4 and up feature the Editable Polygon object, which simplifies most mesh editing operations, and provides subdivision smoothing at customizable levels        SONY VAIO VGN-FZ220E Battery .

Version 7 introduced the edit poly modifier, which allows the use of the tools available in the editable polygon object to be used higher in the modifier stack (i.e., on top of other modifications)

NURBS or non-uniform rational B-spline

An alternative to polygons, it gives a smoothed out surface that eliminates the straight edges of a polygon model   SONY VAIO VGN-FZ340E Battery .

NURBS is a mathematically exact representation of freeform surfaces like those used for car bodies and ship hulls, which can be exactly reproduced at any resolution whenever needed. With NURBS, a smooth sphere can be created with only one face  SONY VAIO VGN-FZ430E Battery .

The non-uniform property of NURBS brings up an important point. Because they are generated mathematically, NURBS objects have a parameter space in addition to the 3D geometric space in which they are displayed. Specifically, an array of values called knots specifies the extent of influence of each control vertex (CV) on the curve or surface   SONY VAIO VGN-FZ460E Battery .

Knots are invisible in 3D space and you can't manipulate them directly, but occasionally their behavior affects the visible appearance of the NURBS object. This topic mentions those situations. Parameter space is one-dimensional for curves, which have only a single U dimension topologically, even though they exist geometrically in 3D space     SONY VAIO VGN-FZ480E Battery .

Surfaces have two dimensions in parameter space, called U and V.

NURBS curves and surfaces have the important properties of not changing under the standard geometric affine transformations (Transforms), or under perspective projections   SONY VAIO VGN-FZ4000 Battery .

The CVs have local control of the object: moving a CV or changing its weight does not affect any part of the object beyond the neighboring CVs. (You can override this property by using the Soft Selection controls.) Also, the control lattice that connects CVs surrounds the surface. This is known as the convex hull property   SONY VAIO VGN-FZ31E Battery .

Surface tool/Editable patch object

Surface tool was originally a 3rd party plugin, but Kinetix acquired and included this feature since version 3.0. The surface tool is for creating common 3ds Max splines, and then applying a modifier called "surface." This modifier makes a surface from every 3 or 4 vertices in a grid        SONY VAIO VGN-FZ31B Battery .

This is often seen as an alternative to "mesh" or "nurbs" modeling, as it enables a user to interpolate curved sections with straight geometry (for example a hole through a box shape). Although the surface tool is a useful way to generate parametrically accurate geometry, it lacks the "surface properties" found in the similar Edit Patch modifier   SONY VAIO VGN-FZ31J Battery ,

which enables a user to maintain the original parametric geometry whilst being able to adjust "smoothing groups" between faces.

Predefined primitives

This is a basic method, in which one models something using only boxes, spheres, cones, cylinders and other predefined objects from the list of Predefined Standard Primitives or a list of Predefined Extended Primitives SONY VAIO VGN-FZ31M Battery .

One may also apply boolean operations, including subtract, cut and connect. For example, one can make two spheres which will work as blobs that will connect with each other. These are called metaballs.

Renderosity is an online art community and marketplace for digital artists          SONY VAIO VGN-FZ31Z Battery ,

with special emphasis on computer-generated 3D graphics, 2D graphics, photography and animation. Originally created as a Poser forum, it now has well over half a million members that use a multitude of different pieces of professional digital design software  SONY VAIO VGN-FZ38M Battery .

History

The community was founded in December 1998 under the name PoserForum.com, reflecting the group's original focus on use of the Poser software. The name was changed to Renderosity by community vote in October 1999. Over time, as the community grew and matured, so did the need to focus less on being a Poser centric community     SONY VGP-BPS8 Battery .

Membership

Renderosity has well over 600,000 members. Membership is free for those wishing to upload a single piece of art, or a monthly subscription permits users to upload three pieces of art and gives access to the entire computer graphics community   SONY VGP-BPS13 Battery .

That includes art galleries, tutorials, free downloadable content, discussion forums, artist bio pages, job board, animations, industry news and interviews.

Communities

There are many sub-communities within the site including artists' galleries, tutorials and forums    SONY VGP-BPS13/S Battery .

These cover a range of popluar mainstream 3D modeling and animation products as well as less well known software.

Marketplace

The Renderosity MarketPlace is an online content library for buying or selling computer generated art or, more commonly, components used to generate art, such as clothing for Poser or a building or object for 3DS Max   SONY VGP-BPS13A/B Battery .

In addition, many brokers sell texture packs or add-ons for products created by other brokers. The MarketPlace is open to all Renderosity members and provides a brokerage program for artists interested in selling their digital products. Renderosity's large membership base allows artists access to a huge distribution channel for their products  SONY VGP-BPS13B/B Battery .

The top selling vendors are rewarded with various awards given out at the end of each year. Initially the only award given out was the Vendor of the Year - which was given to the vendor who had the most sales for the year. This has since been expanded to include the top selling new member that year (Rookie of the Year)   SONY VGP-BPS13A/S Battery ,

the top selling product of the year (Most Valuable Product), and the vendor with the most number of products sold (All Star).

Site design

Renderosity is owned by Bondware, Inc. who provide the hosting and basic design of the site. Every two years, Renderosity holds a contest with its members to redesign the graphics of the website        SONY VGP-BPS13AS Battery .

Applicants submit their entries and the winner is selected by members of the community. Site design changes have occurred in 2001, 2003, 2005 and 2007.

A graphics processing unit or GPU (also occasionally called visual processing unit or VPU) is a specialized microprocessor that offloads and accelerates graphics rendering from the central (micro-)processor   Dell Inspiron 1320n Battery .

It is used in embedded systems, mobile phones, personal computers, workstations, and game consoles. Modern GPUs are very efficient at manipulating computer graphics, and their highly parallel structure makes them more effective than general-purpose CPUs for a range of complex algorithms   Dell Inspiron 1464 Battery .

In a personal computer, a GPU can be present on a video card, or it can be on the motherboard, or as in certain Core Intel CPUs, on a CPU die. More than 90% of new desktop and notebook computers have integrated GPUs, which are usually far less powerful than those on a dedicated video card       Dell Inspiron 1564 Battery .

The term was defined and popularized by Nvidia in 1999, who marketed the GeForce 256 as "the world's first 'GPU', or Graphics Processing Unit, a single-chip processor with integrated transform, lighting, triangle setup/clipping, and rendering engines that is capable of processing a minimum of 10 million polygons per second     Dell Inspiron 1764 Battery .

" Rival ATI Technologies coined the term visual processing unit or VPU with the release of the Radeon 9700 in 2002.

Graphics accelerators

A GPU (Graphics Processing Unit) is a processor attached to a graphics card dedicated to calculating floating point operations  Dell Studio 1450 Battery .

A graphics accelerator incorporates custom microchips which contain special mathematical operations commonly used in graphics rendering. The efficiency of the microchips therefore determines the effectiveness of the graphics accelerator. They are mainly used for playing 3D games or high-end 3D rendering      Dell Studio 1457 Battery .

A GPU implements a number of graphics primitive operations in a way that makes running them much faster than drawing directly to the screen with the host CPU. The most common operations for early 2D computer graphics include the BitBLT operation, combining several bitmap patterns using a raster op       Dell Latitude D610 Battery ,

usually in special hardware called a "blitter", and operations for drawing rectangles, triangles, circles, and arcs. Modern GPUs also have support for 3D computer graphics, and typically include digital video–related functions      Toshiba NB100 Battery .

1970s

The ANTIC and CTIA chips provided for hardware control of mixed graphics and text modes, sprite positioning and display (a form of hardware blitting), and other effects on Atari 8-bit computers. The ANTIC chip was a special purpose processor for mapping (in a programmable fashion) text and graphics data to the video output   Toshiba Satellite M65 battery .

The designer of the ANTIC chip, Jay Miner, subsequently designed the graphics chip for the Commodore Amiga.

1980s

The IBM Professional Graphics Controller was one of the very first 2D/3D graphics accelerators available for the IBM PC  Toshiba Satellite M60 battery .

Released in 1984, 10 years before hardware 3D acceleration became a standard, its high price (~$4500 USD @ 1984 currency), slow processor (8088-2 running at 8 MHz), and lack of compatibility with then-current commercial programs made it unable to succeed in the mass-market     Dell Latitude D830 Battery .

The Commodore Amiga was the first mass-market computer to include a blitter in its video hardware, and IBM's 8514 graphics system was one of the first PC video cards to implement 2D primitives in hardware.

The Amiga was unique, for the time, in that it featured what would now be recognized as a full graphics accelerator  Dell Latitude D620 Battery ,

offloading practically all video generation functions to hardware, including line drawing, area fill, block image transfer, and a graphics coprocessor with its own (primitive) instruction set. Prior to this (and quite some time after on most systems) a general purpose CPU had to handle every aspect of drawing the display  Dell Inspiron Mini 10 Battery .

1990s

In 1991, S3 Graphics introduced the first single-chip 2D accelerator, the S3 86C911, which its designers named after the Porsche 911 as an indication of the performance increase it promised        Sony VGN-FW11S Battery .

The 86C911 spawned a host of imitators: by 1995, all major PC graphics chip makers had added 2D acceleration support to their chips. By this time, fixed-function Windows accelerators had surpassed expensive general-purpose graphics coprocessors in Windows performance, and these coprocessors faded away from the PC market       Sony VGN-FW11M Battery .

Throughout the 1990s, 2D GUI acceleration continued to evolve. As manufacturing capabilities improved, so did the level of integration of graphics chips. Additional application programming interfaces (APIs) arrived for a variety of tasks, such as Microsoft's WinG graphics library for Windows 3.x   Sony VGN-FW139E/H battery ,

and their laterDirectDraw interface for hardware acceleration of 2D games within Windows 95 and later.

In the early and mid-1990s, CPU-assisted real-time 3D graphics were becoming increasingly common in computer and console games, which led to an increasing public demand for hardware-accelerated 3D graphics   Dell Latitude E5400 Battery .

Early examples of mass-marketed 3D graphics hardware can be found in fifth generation video game consoles such as PlayStation and Nintendo 64. In the PC world, notable failed first-tries for low-cost 3D graphics chips were the S3 ViRGE, ATIRage, and MatroxMystique Dell Latitude E4200 Battery .

These chips were essentially previous-generation 2D accelerators with 3D features bolted on. Many were even pin-compatiblewith the earlier-generation chips for ease of implementation and minimal cost. Initially, performance 3D graphics were possible only with discrete boards dedicated to accelerating 3D functions (and lacking 2D GUI acceleration entirely) such as the 3dfx Voodoo Dell Inspiron 300M Battery .

However, as manufacturing technology again progressed, video, 2D GUI acceleration, and 3D functionality were all integrated into one chip. Rendition's Verite chipsets were the first to do this well enough to be worthy of note.

OpenGL appeared in the early 90s as a professional graphics API, but originally suffered from performance issues which allowed the Glide API to step in and become a dominant force on the PC in the late 90s         Dell Vostro A840 Battery .

However these issues were quickly overcome and the Glide API fell by the wayside. Software implementations of OpenGL were common during this time although the influence of OpenGL eventually led to widespread hardware support. Over time a parity emerged between features offered in hardware and those offered in OpenGL     Dell Studio 1737 battery .

DirectX became popular among Windows game developers during the late 90s. Unlike OpenGL, Microsoft insisted on providing strict one-to-one support of hardware. The approach made DirectX less popular as a stand alone graphics API initially since many GPUs provided their own specific features       Dell Inspiron E1505 battery ,

which existing OpenGL applications were already able to benefit from, leaving DirectX often one generation behind. (See: Comparison of OpenGL and Direct3D).

Over time Microsoft began to work more closely with hardware developers, and started to target the releases of DirectX with those of the supporting graphics hardware         Dell RM791 battery .

Direct3D 5.0 was the first version of the burgeoning API to gain widespread adoption in the gaming market, and it competed directly with many more hardware specific, often proprietary graphics libraries, while OpenGL maintained a strong following. Direct3D 7.0 introduced support for hardware-accelerated transform and lighting (T&L) for Direct3D        Dell XPS M1530 battery ,

while OpenGL already had this capability already exposed from the beginning. 3D accelerators moved beyond being just simple rasterizers to add another significant hardware stage to the 3D rendering pipeline. The NVIDIA GeForce 256 (also known as NV10) was the first consumer-level card on the market with hardware-accelerated T&L   Dell XPS M2010 battery ,

while professional 3D cards already had this capability. Hardware transform and lighting, both already existing features of OpenGL, came to consumer-level hardware in the 90s and set the precedent for later pixel shader and vertex shader units which were far more flexible and programmable       Acer Aspire One battery .

2000 to present

With the advent of the OpenGL API and similar functionality in DirectX, GPUs added programmable shading to their capabilities. Each pixel could now be processed by a short program that could include additional image textures as inputs, and each geometric vertex could likewise be processed by a short program before it was projected onto the screen  Toshiba Satellite P10 Battery .

NVIDIA was first to produce a chip capable of programmable shading, the GeForce 3 (code named NV20). By October 2002, with the introduction of the ATI Radeon 9700 (also known as R300), the world's first Direct3D 9.0 accelerator    SONY VGN-FZ210CE Battery,

pixel and vertex shaders could implement looping and lengthy floating point math, and in general were quickly becoming as flexible as CPUs, and orders of magnitude faster for image-array operations. Pixel shading is often used for things like bump mapping, which adds texture, to make an object look shiny, dull, rough, or even round or extruded        Dell Precision M70 Battery .

As the processing power of GPUs has increased, so has their demand for electrical power. High performance GPUs often consume more energy than current CPUs.  See also performance per wattand quiet PC.

Today, parallel GPUs have begun making computational inroads against the CPU, and a subfield of research, dubbed GPU Computing or GPGPU for General Purpose Computing on GPU, has found its way into fields as diverse as oil exploration, scientific image processing, linear algebra, statistics,  3D reconstruction and even stock options pricing determination   Toshiba Satellite L305 Battery .

Nvidia's CUDA platform is the most widely adopted programming model for GPU computing, with OpenCL also being offered as an open standard.

GPU companies

Many companies have produced GPUs under a number of brand names. In 2008, Intel, NVIDIA and AMD/ATI were the market share leaders, with 49.4%, 27.8% and 20.6% market share respectively        Toshiba Satellite T4900 Battery .

However, those numbers include Intel's integrated graphics solutions as GPUs. Not counting those numbers, NVIDIA and ATI control nearly 100% of the market. In addition, S3 Graphics,VIA Technologies  and Matrox  produce GPUs   Toshiba PA3399U-2BRS battery .

Computational functions

Modern GPUs use most of their transistors to perform calculations related to 3D computer graphics. They were initially used to accelerate the memory-intensive work of texture mapping and renderingpolygons, later adding units to accelerate geometric calculations such as the rotation and translation of vertices into different coordinate systems  Toshiba Satellite A200 Battery .

Recent developments in GPUs include support forprogrammable shaders which can manipulate vertices and textures with many of the same operations supported by CPUs, oversampling and interpolation techniques to reduce aliasing, and very high-precision color spaces      Toshiba Satellite 1200 Battery .

Because most of these computations involve matrix and vector operations, engineers and scientists have increasingly studied the use of GPUs for non-graphical calculations.

In addition to the 3D hardware, today's GPUs include basic 2D acceleration and framebuffer capabilities (usually with a VGA compatibility mode)     Toshiba Satellite M300 Battery .

GPU accelerated video decoding

Most GPUs made since 1995 support the YUV color space and hardware overlays, important for digital video playback, and many GPUs made since 2000 also support MPEG primitives such as motion compensation and iDCT   SONY VGP-BPS13A/Q Battery ,

this process of hardware accelerated video decoding, where portions of the video decoding process and video post-processing are offloaded to the GPU hardware, is commonly referred to as "GPU accelerated video decoding", "GPU assisted video decoding", "GPU hardware accelerated video decoding" or "GPU hardware assisted video decoding"  SONY VGP-BPS13A/Q Battery .

More recent graphics cards even decode high-definition video on the card, offloading the central processing unit. The most common API's for GPU accelerated video decoding are DxVA for Microsoft Windows operating-system, and VDPAU, VAAPI, XvMC, and XvBA for Linux and UNIX based operating-system  SONY VGP-BPS13B/Q Battery .

All except XvMC are capable of decoding videos encoded with MPEG-1, MPEG-2,MPEG-4 ASP (MPEG-4 Part 2), MPEG-4 AVC (H.264 / DivX 6), VC-1, WMV3/WMV9, Xvid / OpenDivX (DivX 4), and DivX 5 codecs, while XvMC is only capable of decoding MPEG-1 and MPEG-2   SONY VGP-BPS13B/Q Battery .

Video decoding processes that can be accelerated

The video decoding processes that can be accelerated by today's modern GPU hardware are:

• Motion compensation (mocomp)
• Inverse discrete cosine transform (iDCT)        SONY VGP-BPS13/Q Battery
  • Inverse telecine 3:2 and 2:2 pull-down correction
• Inverse modified discrete cosine transform (iMDCT)
• In-loop deblocking filter
• Intra-frame prediction           SONY VGP-BPS13/Q Battery
• Inverse quantization (IQ)
• Variable-Length Decoding (VLD), more commonly known as slice-level acceleration
• Spatial-temporal deinterlacing and automatic interlace/progressive source detection
• Bitstream processing (CAVLC/CABAC)         SONY VGP-BPS21A/B Battery .

GPU forms

Dedicated graphics cards

The GPUs of the most powerful class typically interface with the motherboard by means of an expansion slot such as PCI Express (PCIe) or Accelerated Graphics Port (AGP) and can usually be replaced or upgraded with relative ease, assuming the motherboard is capable of supporting the upgrade        SONY VGP-BPS21/S Battery .

A few graphics cards still use Peripheral Component Interconnect (PCI) slots, but their bandwidth is so limited that they are generally used only when a PCIe or AGP slot is not available.

A dedicated GPU is not necessarily removable, nor does it necessarily interface with the motherboard in a standard fashion  SONY VGP-BPS21B Battery .

The term "dedicated" refers to the fact that dedicated graphics cards haveRAM that is dedicated to the card's use, not to the fact that most dedicated GPUs are removable. Dedicated GPUs for portable computers are most commonly interfaced through a non-standard and often proprietary slot due to size and weight constraints   SONY VGP-BPS21A Battery .

Such ports may still be considered PCIe or AGP in terms of their logical host interface, even if they are not physically interchangeable with their counterparts.

Technologies such as SLI by NVIDIA and CrossFire by ATI allow multiple GPUs to be used to draw a single image, increasing the processing power available for graphics   SONY VGP-BPS21 Battery .

Integrated graphics solutions

Integrated graphics solutions, shared graphics solutions, or Integrated graphics processors (IGP) utilize a portion of a computer's system RAM rather than dedicated graphics memory. Exceptions are AMD's IGPs that use dedicated sideport memory on certain motherboards        Sony VGP-BPS21A/B Battery .

Computers with integrated graphics account for 90% of all PC shipments.These solutions are less costly to implement than dedicated graphics solutions, but are less capable. Historically, integrated solutions were often considered unfit to play 3D games or run graphically intensive programs but could run less intensive programs such as Adobe Flash  Sony VGP-BPS21/S Battery .

Examples of such IGPs would be offerings from SiS and VIA circa 2004.However, today's integrated solutions such as AMD's Radeon HD 3200 (AMD 780G chipset) and NVIDIA's GeForce 8200 (nForce 710|NVIDIA nForce 730a) are more than capable of handling 2D graphics from Adobe Flash or low stress 3D graphics  Sony VGP-BPS21B Battery .

However, most integrated graphics still struggle with high-end video games. Chips like the Nvidia GeForce 9400M in Apple's MacBook and MacBook Pro and AMD's Radeon HD 3300 (AMD 790GX) have an improved performance, but still lag behind dedicated graphics cards      Sony VGP-BPS21A Battery .

Modern desktop motherboards often include an integrated graphics solution and have expansion slots available to add a dedicated graphics card later.

As a GPU is extremely memory intensive, an integrated solution may find itself competing for the already relatively slow system RAM with the CPU, as it has minimal or no dedicated video memory   Sony VGP-BPS21 Battery .

System RAM may be 2 Gbit/s to 12.8 Gbit/s, yet dedicated GPUs enjoy between 10 Gbit/s to over 100 Gbit/s of bandwidth depending on the model.

Older integrated graphics chipsets lacked hardware transform and lighting, but newer ones include it   Sony Vaio PCG-5G2L Battery .

Hybrid solutions

This newer class of GPUs competes with integrated graphics in the low-end desktop and notebook markets. The most common implementations of this are ATI's HyperMemory and NVIDIA'sTurboCache. Hybrid graphics cards are somewhat more expensive than integrated graphics, but much less expensive than dedicated graphics cards  Sony Vaio PCG-5G3L Battery .

These share memory with the system and have a small dedicated memory cache, to make up for the high latency of the system RAM. Technologies within PCI Express can make this possible. While these solutions are sometimes advertised as having as much as 768MB of RAM, this refers to how much can be shared with the system memory   Sony Vaio PCG-5J1L Battery .

Stream Processing and General Purpose GPUs (GPGPU)

A new concept is to use a general purpose graphics processing unit as a modified form of stream processor. This concept turns the massive floating-point computational power of a modern graphics accelerator's shader pipeline into general-purpose computing power, as opposed to being hard wired solely to do graphical operations          Sony Vaio PCG-5K2L Battery .

In certain applications requiring massive vector operations, this can yield several orders of magnitude higher performance than a conventional CPU. The two largest discrete (see "Dedicated graphics cards" above) GPU designers, ATI and NVIDIA, are beginning to pursue this new approach with an array of applications         Sony Vaio PCG-5J2L Battery .

Both nVidia and ATI have teamed with Stanford University to create a GPU-based client for the Folding@Home distributed computing project, for protein folding calculations. In certain circumstances the GPU calculates forty times faster than the conventional CPUs traditionally used by such applications       Sony Vaio PCG-5K1L Battery .

Furthermore, GPU-based high performance computers are starting to play a significant role in large-scale modelling. Three of the 5 most powerful supercomputers in the world take advantage of GPU acceleration. This includes the current leader as of October 2010, Tianhe-1A, which uses the NVIDIA Tesla platform     Sony Vaio PCG-5L1L Battery .

Recently NVidia began releasing cards supporting an API extension to the C programming language CUDA ("Compute Unified Device Architecture"), which allows specified functions from a normal C program to run on the GPU's stream processors   Sony Vaio PCG-6S2L Battery .

This makes C programs capable of taking advantage of a GPU's ability to operate on large matrices in parallel, while still making use of the CPU when appropriate. CUDA is also the first API to allow CPU-based applications to access directly the resources of a GPU for more general purpose computing without the limitations of using a graphics API   Sony Vaio PCG-6S3L Battery .

Since 2005 there has been interest in using the performance offered by GPUs for evolutionary computation in general, and for accelerating the fitness evaluation in genetic programming in particular. Most approaches compile linear or tree programs on the host PC and transfer the executable to the GPU to be run        Sony Vaio PCG-6V1L Battery .

Typically the performance advantage is only obtained by running the single active program simultaneously on many example problems in parallel, using the GPU's SIMD architecture.However, substantial acceleration can also be obtained by not compiling the programs, and instead transferring them to the GPU, to be interpreted there       Sony Vaio PCG-6W1L Battery .

Acceleration can then be obtained by either interpreting multiple programs simultaneously, simultaneously running multiple example problems, or combinations of both. A modern GPU (e.g. 8800 GTX or later) can readily simultaneously interpret hundreds of thousands of very small programs       Sony Vaio PCG-6W2L Battery .