Backward compatibility
Encyclopedia
In the context of telecommunications and computing
, a device or technology is said to be backward or downward compatible if it can work with input generated by an older device. If products designed for the new standard can receive, read, view or play older standards or formats, then the product is said to be backward-compatible; examples of such a standard include data formats and communication protocols
.
The reverse is forward compatibility
, which implies that old devices allow (or are expected to allow) data formats generated by new (or future) devices, perhaps without supporting all new features. A standard supports forward compatibility if older product versions can receive, read, view, or play the new standard.
For example, the introduction of FM stereo transmission allowed backward compatibility since new FM radio receivers could receive monaural
signals generated by old transmitters. It also allowed forward compatibility, since old monaural FM radio receivers still could receive a signal from a new transmitter.
In programming languages, backward compatibility refers to the ability of a compiler for version N of the language to accept programs or data that worked under version N - 1. (By this definition, if previous versions (N - 1, N - 2, etc.) were also backward compatible, which is often the case, then, by induction, version N will also accept input that worked under any prior version after, and including, the latest one that was not backward compatible. However, in practice, features are often deprecated and support is dropped in a later release, which is yet thought of as backward compatible.)
In other contexts, a product or a technology is said to be backward compatible when it is able to fully take the place of an older product, by inter-operating with products that were designed for the older product.
A data format is also said to be backward compatible with its predecessor if every message or file that is valid under the old format is also valid, and retains its meaning, under the new.
Backward compatibility is the special case of compatibility in which the new component has a direct historical ancestral relationship with the old component. If this special relationship does not exist then it not usually spoken of as "backward" compatibility but is instead just "compatible"—a consistent interface allowing interoperability
between components and products that were each developed separately.
In the case of a program that creates document files, a new version of that program ("v2") is said to be backward compatible with the old version of the program ("v1") when it can both read and write documents that work with v1. Everything that v1 could do must also be possible with v2, including saving documents that can be read by v1 (which is something that v1 could do.)
If a newer software version cannot save files that can be read by the older version, it is not backward compatible with the older version, although it may provide an irreversible upgrade
capability for the old files. This situation has often been used strategically by software vendors to force customers to purchase upgrades since, over time, the number of data files usable by an old version diminishes at a rate proportional to the number of other customers that have upgraded (assuming that all customers generate files at the same the average rate.)
Levels of compatibility vary. In software, binary compatibility and source compatibility are distinguishable. Binary compatibility means that programs can work correctly with the new version of this library without requiring recompilation
. Source compatibility requires recompilation but no changes to the source code.
Many platforms rely on emulation
, the simulation of an older platform in software, to achieve backward compatibility.
"), then the new system may be referred to as "bugwards-compatible".
Computing
Computing is usually defined as the activity of using and improving computer hardware and software. It is the computer-specific part of information technology...
, a device or technology is said to be backward or downward compatible if it can work with input generated by an older device. If products designed for the new standard can receive, read, view or play older standards or formats, then the product is said to be backward-compatible; examples of such a standard include data formats and communication protocols
Communications protocol
A communications protocol is a system of digital message formats and rules for exchanging those messages in or between computing systems and in telecommunications...
.
The reverse is forward compatibility
Forward compatibility
Forward compatibility or upward compatibility is a compatibility concept for systems design, as e.g. backward compatibility. Forward compatibility aims at the ability of a design to gracefully accept input intended for later versions of itself...
, which implies that old devices allow (or are expected to allow) data formats generated by new (or future) devices, perhaps without supporting all new features. A standard supports forward compatibility if older product versions can receive, read, view, or play the new standard.
For example, the introduction of FM stereo transmission allowed backward compatibility since new FM radio receivers could receive monaural
Monaural
Monaural or monophonic sound reproduction is single-channel. Typically there is only one microphone, one loudspeaker, or channels are fed from a common signal path...
signals generated by old transmitters. It also allowed forward compatibility, since old monaural FM radio receivers still could receive a signal from a new transmitter.
In programming languages, backward compatibility refers to the ability of a compiler for version N of the language to accept programs or data that worked under version N - 1. (By this definition, if previous versions (N - 1, N - 2, etc.) were also backward compatible, which is often the case, then, by induction, version N will also accept input that worked under any prior version after, and including, the latest one that was not backward compatible. However, in practice, features are often deprecated and support is dropped in a later release, which is yet thought of as backward compatible.)
In other contexts, a product or a technology is said to be backward compatible when it is able to fully take the place of an older product, by inter-operating with products that were designed for the older product.
A data format is also said to be backward compatible with its predecessor if every message or file that is valid under the old format is also valid, and retains its meaning, under the new.
Description
Backward compatibility is a relationship between two components, rather than being an attribute of just one of them. More generally, a new component is said to be backward compatible if it provides all of the functionality of the old component.Backward compatibility is the special case of compatibility in which the new component has a direct historical ancestral relationship with the old component. If this special relationship does not exist then it not usually spoken of as "backward" compatibility but is instead just "compatible"—a consistent interface allowing interoperability
Interoperability
Interoperability is a property referring to the ability of diverse systems and organizations to work together . The term is often used in a technical systems engineering sense, or alternatively in a broad sense, taking into account social, political, and organizational factors that impact system to...
between components and products that were each developed separately.
In the case of a program that creates document files, a new version of that program ("v2") is said to be backward compatible with the old version of the program ("v1") when it can both read and write documents that work with v1. Everything that v1 could do must also be possible with v2, including saving documents that can be read by v1 (which is something that v1 could do.)
If a newer software version cannot save files that can be read by the older version, it is not backward compatible with the older version, although it may provide an irreversible upgrade
Upgrade
The term upgrade refers to the replacement of a product with a newer version of the same product. It is most often used in computing and consumer electronics, generally meaning a replacement of hardware, software or firmware with a newer or better version, in order to bring the system up to date...
capability for the old files. This situation has often been used strategically by software vendors to force customers to purchase upgrades since, over time, the number of data files usable by an old version diminishes at a rate proportional to the number of other customers that have upgraded (assuming that all customers generate files at the same the average rate.)
Levels of compatibility vary. In software, binary compatibility and source compatibility are distinguishable. Binary compatibility means that programs can work correctly with the new version of this library without requiring recompilation
Compiler
A compiler is a computer program that transforms source code written in a programming language into another computer language...
. Source compatibility requires recompilation but no changes to the source code.
Many platforms rely on emulation
Emulator
In computing, an emulator is hardware or software or both that duplicates the functions of a first computer system in a different second computer system, so that the behavior of the second system closely resembles the behavior of the first system...
, the simulation of an older platform in software, to achieve backward compatibility.
Bugwards Compatible
If a newer system is attempting to achieve integration with an older system which has known flaws (or "bugsSoftware bug
A software bug is the common term used to describe an error, flaw, mistake, failure, or fault in a computer program or system that produces an incorrect or unexpected result, or causes it to behave in unintended ways. Most bugs arise from mistakes and errors made by people in either a program's...
"), then the new system may be referred to as "bugwards-compatible".
Examples
- The NTSCNTSCNTSC, named for the National Television System Committee, is the analog television system that is used in most of North America, most of South America , Burma, South Korea, Taiwan, Japan, the Philippines, and some Pacific island nations and territories .Most countries using the NTSC standard, as...
color broadcast system was engineered by RCARCARCA Corporation, founded as the Radio Corporation of America, was an American electronics company in existence from 1919 to 1986. The RCA trademark is currently owned by the French conglomerate Technicolor SA through RCA Trademark Management S.A., a company owned by Technicolor...
to be backward compatible with black-and-whiteBlack-and-whiteBlack-and-white, often abbreviated B/W or B&W, is a term referring to a number of monochrome forms in visual arts.Black-and-white as a description is also something of a misnomer, for in addition to black and white, most of these media included varying shades of gray...
NTSC television sets. - Most Blu-ray disc drivesBlu-ray DiscBlu-ray Disc is an optical disc storage medium designed to supersede the DVD format. The plastic disc is 120 mm in diameter and 1.2 mm thick, the same size as DVDs and CDs. Blu-ray Discs contain 25 GB per layer, with dual layer discs being the norm for feature-length video discs...
are able to play standard CD and DVDDVDA DVD is an optical disc storage media format, invented and developed by Philips, Sony, Toshiba, and Panasonic in 1995. DVDs offer higher storage capacity than Compact Discs while having the same dimensions....
discs and most DVD drivesDVDA DVD is an optical disc storage media format, invented and developed by Philips, Sony, Toshiba, and Panasonic in 1995. DVDs offer higher storage capacity than Compact Discs while having the same dimensions....
are able to play standard CDs. - Numerous video game consoles are backward compatible and are able to play the games created for predecessor consoles:
- The Atari 7800Atari 7800The Atari 7800 ProSystem, or simply the Atari 7800, is a video game console re-released by Atari Corporation in January 1986. The original release had occurred two years earlier under Atari Inc. The 7800 had originally been designed to replace Atari Inc.'s Atari 5200 in 1984, but was temporarily...
is backward compatible with almost all Atari 2600Atari 2600The Atari 2600 is a video game console released in October 1977 by Atari, Inc. It is credited with popularizing the use of microprocessor-based hardware and cartridges containing game code, instead of having non-microprocessor dedicated hardware with all games built in...
games. - The Game Boy AdvanceGame Boy AdvanceThe is a 32-bit handheld video game console developed, manufactured, and marketed by Nintendo. It is the successor to the Game Boy Color. It was released in Japan on March 21, 2001; in North America on June 11, 2001; in Australia and Europe on June 22, 2001; and in the People's Republic of China...
line (except the Game Boy MicroGame Boy Microis a handheld game console developed and manufactured by Nintendo. It was first released in September 2005 in the market. The system is the last console of the Game Boy line...
) is backward compatible with previous Game Boy systemsGame Boy lineThe line is a line of battery-powered handheld game console sold by Nintendo. It is one of the world's best-selling game system lines with a combined 200+ million units sold worldwide....
, meaning all Game BoyGame BoyThe , is an 8-bit handheld video game device developed and manufactured by Nintendo. It was released in Japan on , in North America in , and in Europe on...
and Game Boy ColorGame Boy ColorThe is Nintendo's successor to the 8-bit Game Boy handheld game console, and was released on October 21, 1998 in Japan, November 19, 1998 in North America, November 23, 1998 in Europe and November 27, 1998 in the United Kingdom. It features a color screen and is slightly thicker and taller than...
titles are playable on this system. - The Nintendo DSNintendo DSThe is a portable game console produced by Nintendo, first released on November 21, 2004. A distinctive feature of the system is the presence of two separate LCD screens, the lower of which is a touchscreen, encompassed within a clamshell design, similar to the Game Boy Advance SP...
and the Nintendo DS LiteNintendo DS LiteThe is a dual-screen handheld game console developed and manufactured by Nintendo. It is a slimmer, brighter, and more lightweight redesign of the Nintendo DS, designed to be aesthetically sleeker, while taking styling cues from the Game Boy Advance SP, and to appeal to broader commercial audiences...
are backward compatible with all Game Boy Advance games. - The Nintendo 3DSNintendo 3DSThe is a portable game console produced by Nintendo. The autostereoscopic device is able to project stereoscopic 3D effects without the use of 3D glasses or any additional accessories. The Nintendo 3DS features backward compatibility with Nintendo DS series software, including Nintendo DSi software...
is backward compatible with the Nintendo DSNintendo DSThe is a portable game console produced by Nintendo, first released on November 21, 2004. A distinctive feature of the system is the presence of two separate LCD screens, the lower of which is a touchscreen, encompassed within a clamshell design, similar to the Game Boy Advance SP...
and Nintendo DSiNintendo DSiThe is a handheld game system created by Nintendo and launched in 2008 and 2009 in Japan, North America, PAL territories, and other regions. It is the third iteration of the Nintendo DS, and its primary market rival is Sony's PlayStation Portable...
software. - The PlayStation 2PlayStation 2The PlayStation 2 is a sixth-generation video game console manufactured by Sony as part of the PlayStation series. Its development was announced in March 1999 and it was first released on March 4, 2000, in Japan...
is backward compatible with most of the original PlayStationPlayStationThe is a 32-bit fifth-generation video game console first released by Sony Computer Entertainment in Japan on December 3, .The PlayStation was the first of the PlayStation series of consoles and handheld game devices. The PlayStation 2 was the console's successor in 2000...
library. Additionally, the initial PlayStation 3PlayStation 3The is the third home video game console produced by Sony Computer Entertainment and the successor to the PlayStation 2 as part of the PlayStation series. The PlayStation 3 competes with Microsoft's Xbox 360 and Nintendo's Wii as part of the seventh generation of video game consoles...
model is backward compatible with most PlayStation and PlayStation 2 games. This is provided by the inclusion of the original Emotion EngineEmotion EngineThe Emotion Engine is a CPU developed and manufactured by Sony Computer Entertainment and Toshiba for use in the Sony PlayStation 2 video game console, as well as early PlayStation 3 models sold in Japan and North America...
chip that is built inside the PS3. However, subsequent models removed this and the "Graphics Synthesizer" GPU, thus removing support for PS2 titles, but still able to play most original PS games. - The PSPPSPPSP most commonly refers to the PlayStation Portable, a handheld game console produced by Sony Computer Entertainment.PSP may also refer to:-Computing and programming:*Corel Paint Shop Pro, a graphics editor...
is backward compatible with psone games using remote play or downloaded. - The PS Vita is backward compatible with PSPPSPPSP most commonly refers to the PlayStation Portable, a handheld game console produced by Sony Computer Entertainment.PSP may also refer to:-Computing and programming:*Corel Paint Shop Pro, a graphics editor...
games, mini, psone and neo geo games downloaded off the ps store. - The Xbox 360Xbox 360The Xbox 360 is the second video game console produced by Microsoft and the successor to the Xbox. The Xbox 360 competes with Sony's PlayStation 3 and Nintendo's Wii as part of the seventh generation of video game consoles...
is backward compatible with some XboxXboxThe Xbox is a sixth-generation video game console manufactured by Microsoft. It was released on November 15, 2001 in North America, February 22, 2002 in Japan, and March 14, 2002 in Australia and Europe and is the predecessor to the Xbox 360. It was Microsoft's first foray into the gaming console...
games via software emulation. - The WiiWiiThe Wii is a home video game console released by Nintendo on November 19, 2006. As a seventh-generation console, the Wii primarily competes with Microsoft's Xbox 360 and Sony's PlayStation 3. Nintendo states that its console targets a broader demographic than that of the two others...
is backward compatible with all games from the previous NintendoNintendois a multinational corporation located in Kyoto, Japan. Founded on September 23, 1889 by Fusajiro Yamauchi, it produced handmade hanafuda cards. By 1963, the company had tried several small niche businesses, such as a cab company and a love hotel....
system, the Nintendo GameCubeNintendo GameCubeThe , officially abbreviated to NGC in Japan and GCN in other regions, is a sixth generation video game console released by Nintendo on September 15, 2001 in Japan, November 18, 2001 in North America, May 3, 2002 in Europe, and May 17, 2002 in Australia...
, due to its being based on the PowerPCPowerPCPowerPC is a RISC architecture created by the 1991 Apple–IBM–Motorola alliance, known as AIM...
, the same base as the latter. - The Wii U will be backward compatible with all games from the previous Nintendo system, The Nintendo Wii.
- The Atari 7800
- Microsoft WindowsMicrosoft WindowsMicrosoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...
contains application compatibility shims to make the platform compatible with most software from earlier 32-bit and 16-bit versions (e.g. CivilizationCivilization (computer game)Sid Meier's Civilization is a turn-based strategy "4X"-type strategy video game created by Sid Meier and Bruce Shelley for MicroProse in 1991. The game's objective is to "Build an empire to stand the test of time": it begins in 4000 BC and the players attempt to expand and develop their empires...
(circa 1991, designed for Windows 3.0Windows 3.0Windows 3.0, a graphical environment, is the third major release of Microsoft Windows, and was released on 22 May 1990. It became the first widely successful version of Windows and a rival to Apple Macintosh and the Commodore Amiga on the GUI front...
) running on Windows Vista). - The IntelApple-Intel architectureThe Apple–Intel architecture is an unofficial name used for Apple Macintosh personal computers developed and manufactured by Apple Inc. that use Intel x86 processors, rather than the PowerPC and 68k processors used in their predecessors.-Technologies:...
versions of Mac OS XMac OS XMac OS X is a series of Unix-based operating systems and graphical user interfaces developed, marketed, and sold by Apple Inc. Since 2002, has been included with all new Macintosh computer systems...
from versions 10.4 (Tiger) to 10.6 (Snow Leopard) use RosettaRosetta (software)Rosetta was a lightweight and dynamic binary translator for Mac OS X which Apple released in 2006 when it transitioned the Macintosh from PowerPC to Intel processors. It allowed pre-existing software to run on the new systems without modification....
, a binary translationBinary translationIn computing, binary translation is the emulation of one instruction set by another through translation of code. Sequences of instructions are translated from the source to the target instruction set...
program that allows applications meant for use on PowerPC Macs to run on Apple systems that use Intel processors. (The newest OS X version, LionMac OS X LionMac OS X Lion is the eighth and current major release of Mac OS X, Apple's desktop and server operating system for Macintosh computers....
, does not use Rosetta and thus cannot run PowerPC applications.) - Microsoft WordMicrosoft WordMicrosoft Word is a word processor designed by Microsoft. It was first released in 1983 under the name Multi-Tool Word for Xenix systems. Subsequent versions were later written for several other platforms including IBM PCs running DOS , the Apple Macintosh , the AT&T Unix PC , Atari ST , SCO UNIX,...
2000 was backward compatible with Word 97 because it could read and write files in Word 97 format, with the understanding that features unique to Word 2000 would not appear in Word 97. At the same time, Microsoft WordMicrosoft WordMicrosoft Word is a word processor designed by Microsoft. It was first released in 1983 under the name Multi-Tool Word for Xenix systems. Subsequent versions were later written for several other platforms including IBM PCs running DOS , the Apple Macintosh , the AT&T Unix PC , Atari ST , SCO UNIX,...
, ExcelMicrosoft ExcelMicrosoft Excel is a proprietary commercial spreadsheet application written and distributed by Microsoft for Microsoft Windows and Mac OS X. It features calculation, graphing tools, pivot tables, and a macro programming language called Visual Basic for Applications...
, PowerPointMicrosoft PowerPointMicrosoft PowerPoint, usually just called PowerPoint, is a non-free commercial presentation program developed by Microsoft. It is part of the Microsoft Office suite, and runs on Microsoft Windows and Apple's Mac OS X operating system...
, AccessMicrosoft AccessMicrosoft Office Access, previously known as Microsoft Access, is a relational database management system from Microsoft that combines the relational Microsoft Jet Database Engine with a graphical user interface and software-development tools. It is a member of the Microsoft Office suite of...
and OneNote, both 2007 and 2010, are also backward compatible with their 97-2003 file formats and features in the same manner. - Several computer operating systemOperating systemAn operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer system...
s have various methods of running software originally designed for older versions or other OSs:- Windows NTWindows NTWindows NT is a family of operating systems produced by Microsoft, the first version of which was released in July 1993. It was a powerful high-level-language-based, processor-independent, multiprocessing, multiuser operating system with features comparable to Unix. It was intended to complement...
and successors have various subsystems to run legacy applications. MS-DOSMS-DOSMS-DOS is an operating system for x86-based personal computers. It was the most commonly used member of the DOS family of operating systems, and was the main operating system for IBM PC compatible personal computers during the 1980s to the mid 1990s, until it was gradually superseded by operating...
and Win16 subsystems (only on i386) can run some applications for those platforms, and it has an OS/2OS/2OS/2 is a computer operating system, initially created by Microsoft and IBM, then later developed by IBM exclusively. The name stands for "Operating System/2," because it was introduced as part of the same generation change release as IBM's "Personal System/2 " line of second-generation personal...
subsystem for running CLI OS/2 applications. - With the introduction of Windows 7 (Business, Ultimate, or Enterprise editions), Windows XP Mode enables full compatibility with older programs supported under Windows XP via Microsoft Virtual PC.
- Windows NT
- The modern Nikon F Mount SLR camera lenses from the late 1970s - present (its design dates back to 1959) can function on the newer Nikon DSLR cameras with some limitations.
- Lenses for the Canon EF mountCanon EF lens mountIntroduced in 1987, the EF lens mount is the standard lens mount on the Canon EOS family of SLR film and digital cameras. EF stands for "Electro-Focus": automatic focusing on EF lenses is handled by a dedicated electric motor built into the lens...
, introduced with the company's EOSCanon EOSThe Canon EOS autofocus 35 mm film and digital SLR camera system was introduced in 1987 with the Canon EOS 650 and is still in production as Canon's current DSLR system...
family of film SLRs in 1987 and used to this day on Canon full-frame and APS-H EOS DSLRs, can function on the company's APS-CAPS-CAdvanced Photo System type-C is an image sensor format approximately equivalent in size to the Advanced Photo System "classic" size negatives...
DSLRs that use the EF-S mountCanon EF-S lens mountThe EF-S lens mount is a derivative of the EF lens mount created for a subset of Canon digital single-lens reflex cameras with APS-C sized image sensors. It was released in 2003. Cameras supporting the EF-S mount are backward-compatible with the EF lens mount and, as such, have a flange focal...
with some limitations. - PCI ExpressPCI ExpressPCI Express , officially abbreviated as PCIe, is a computer expansion card standard designed to replace the older PCI, PCI-X, and AGP bus standards...
2.0 is backward compatible with PCI Express 1.1. - The IBM 7080IBM 7080The IBM 7080 was a variable word length BCD transistor computer in the IBM 700/7000 series commercial architecture line, introduced in August 1961, that provided an upgrade path from the vacuum tube IBM 705 computer....
transistorTransistorA transistor is a semiconductor device used to amplify and switch electronic signals and power. It is composed of a semiconductor material with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor's terminals changes the current...
ized computer was backward compatible with all models of the IBM 705 vacuum tubeVacuum tubeIn electronics, a vacuum tube, electron tube , or thermionic valve , reduced to simply "tube" or "valve" in everyday parlance, is a device that relies on the flow of electric current through a vacuum...
computer.
See also
- Format rotFormat rotIn computer science, "format rot" refers to the loss of data not due to losing information, but due to losing the means to interpret it by either an unavailability of software to parse the format, unavailability of the operating system to run said software, or unavailability of hardware to run said...
- Forward compatibilityForward compatibilityForward compatibility or upward compatibility is a compatibility concept for systems design, as e.g. backward compatibility. Forward compatibility aims at the ability of a design to gracefully accept input intended for later versions of itself...
- Legacy systemLegacy systemA legacy system is an old method, technology, computer system, or application program that continues to be used, typically because it still functions for the users' needs, even though newer technology or more efficient methods of performing a task are now available...
- Software emulation
- Computer compatibilityComputer compatibilityA family of computer models is said to be compatible if certain software that runs on one of the models can also be run on all other models of the family. The computer models may differ in performance, reliability or some other characteristic...
- Shim