Backward compatibility is a property of a system, product, or technology that allows for interoperability with an older legacy system, or with input designed for such a system, especially in telecommunications and computing. Backward compatibility is sometimes also called downward compatibility.r
Interoperability is a characteristic of a product or system, whose interfaces are completely understood, to work with other products or systems, at present or in the future, in either implementation or access, without any restrictions.
In computing, a legacy system is an old method, technology, computer system, or application program, "of, relating to, or being a previous or outdated computer system," yet still in use. Often referencing a system as "legacy" means that it paved the way for the standards that would follow it. This can also imply that the system is out of date or in need of replacement.
In computing, input/output or I/O is the communication between an information processing system, such as a computer, and the outside world, possibly a human or another information processing system. Inputs are the signals or data received by the system and outputs are the signals or data sent from it. The term can also be used as part of an action; to "perform I/O" is to perform an input or output operation.
Modifying a system in a way that does not allow backward compatibility is sometimes called "breaking" backward compatibility.
A complementary concept is forward compatibility. A design that is forward-compatible usually has a roadmap for compatibility with future standards and products.
Forward compatibility or upward compatibility is a design characteristic that allows a system to accept input intended for a later version of itself. The concept can be applied to entire systems, electrical interfaces, telecommunication signals, data communication protocols, file formats, and computer programming languages. A standard supports forward compatibility if a product that complies with earlier versions can "gracefully" process input designed for later versions of the standard, ignoring new parts which it does not understand.
A technology roadmap is a flexible planning technique to support strategic and long-range planning, by matching short-term and long-term goals with specific technology solutions. It is a plan that applies to a new product or process and may include using technology forecasting/technology scouting to identify suitable emerging technologies. It is a known technique to help manage the fuzzy front-end of innovation. It is also expected that roadmapping techniques may help companies to survive in turbulent environments and help them to plan in a more holistic way to include non-financial goals and drive towards a more sustainable development. Here roadmaps can be combined with other corporate foresight methods to facilitate systemic change.
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The associated benefits of backward compatibility are the appeal to an existing user base through an inexpensive upgrade path as well as the network effect, which is particularly important, as it increases the value of goods and services proportionally to the size of the user base.
Upgrading is the process of replacing a product with a newer version of the same product. In computing and consumer electronics an upgrade is generally a replacement of hardware, software or firmware with a newer or better version, in order to bring the system up to date or to improve its characteristics.
In telecommunications, the Network Effectiveness Ratio (NER) measures the ability of a network to deliver a call to the called terminal. Busy signals and other call failure due to user behaviour are counted as "successful call delivery" for NER calculation purposes. Unlike ASR, NER excludes the effects of customer and terminal behaviour. NER is a measure of network quality defined by the ITU.
One example of this is the Sony PlayStation 2 (PS2) which was backward compatible with games for its predecessor PlayStation (PS1). While the selection of PS2 games available at launch was small, sales of the console were nonetheless strong in 2000-2001 thanks to the large library of games for the preceding PS1. This bought time for the PS2 to grow a large installed base and developers to release more quality PS2 games for the crucial 2001 holiday season.
The PlayStation 2 is a home video game console developed and marketed by Sony Computer Entertainment. It was first released in Japan on March 4, 2000, in North America on October 26, 2000, and in Europe and Australia in November 2000, and is the successor to the PlayStation, as well as the second video game console in the PlayStation brand. As a sixth-generation console, the PS2 competed with Sega's Dreamcast, Nintendo's GameCube, and Microsoft's Xbox.
The PlayStation is a home video game console developed and marketed by Sony Computer Entertainment. It was first released on 3 December 1994 in Japan, on 9 September 1995 in North America, on 29 September 1995 in Europe, and on 15 November 1995 in Australia, and was the first of the PlayStation lineup of video game consoles. As a fifth generation console, the PlayStation primarily competed with the Nintendo 64 and the Sega Saturn.
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The associated costs of backward compatibility are a higher bill of materials if hardware is required to support the legacy systems; increased complexity of the product that may lead to longer time to market, technological hindrances, and slowing innovation; and increased expectations from users in terms of compatibility.
A bill of materials or product structure is a list of the raw materials, sub-assemblies, intermediate assemblies, sub-components, parts, and the quantities of each needed to manufacture an end product. A BOM may be used for communication between manufacturing partners or confined to a single manufacturing plant. A bill of materials is often tied to a production order whose issuance may generate reservations for components in the bill of materials that are in stock and requisitions for components that are not in stock.
In commerce, time to market (TTM) is the length of time it takes from a product being conceived until its being available for sale. TTM is important in industries where products are outmoded quickly. A common assumption is that TTM matters most for first-of-a-kind products, but actually the leader often has the luxury of time, while the clock is clearly running for the followers.
A notable example is the Sony PlayStation 3, as the first PS3 iteration was expensive to manufacture in part due to including the Emotion Engine from the preceding PS2 in order to run PS2 games, since the PS3 architecture was completely different from the PS2. Subsequent PS3 hardware revisions have eliminated the Emotion Engine as it saved production costs while removing the ability to run PS2 titles, as Sony found out that backward compatibility was not a major selling point for the PS3. in contrast to the PS2. The PS3's chief competitor, the Microsoft Xbox 360, took a different approach to backward compatibility by using software emulation in order to run games from the first Xbox, rather than including legacy hardware from the original Xbox which was quite different from the Xbox 360, however Microsoft stopped releasing emulation profiles after 2007.
A simple example of both backward and forward compatibility is the introduction of FM radio in stereo. FM radio was initially mono, with only one audio channel represented by one signal. With the introduction of two-channel stereo FM radio, a large number of listeners had only mono FM receivers. Forward compatibility for mono receivers with stereo signals was achieved through sending the sum of both left and right audio channels in one signal and the difference in another signal. That allows mono FM receivers to receive and decode the sum signal while ignoring the difference signal, which is necessary only for separating the audio channels. Stereo FM receivers can receive a mono signal and decode it without the need for a second signal, and they can separate a sum signal to left and right channels if both sum and difference signals are received. Without the requirement for backward compatibility, a simpler method could have been chosen.
Full backward compatibility is particularly important in computer instruction set architectures, one of the most successful being the x86 family of microprocessors. Their full backward compatibility spans back to the 16-bit Intel 8086/8088 processors introduced in 1978. (The 8086/8088, in turn, were designed with easy machine-translatability of programs written for its predecessor in mind, although they were not instruction-set compatible with the 8-bit Intel 8080 processor as of 1974. The Zilog Z80, however, was fully backwards compatible with the Intel 8080.) Fully backwards compatible processors can process the same binary executable software instructions as their predecessors, allowing the use of a newer processor without having to acquire new applications or operating systems. Similarly, the success of the Wi-Fi digital communication standard is attributed to its broad forward and backward compatibility; it became more popular than other standards that were not backward compatible.
Compiler backward compatibility may refer to the ability of a compiler of a newer version of the language to accept programs or data that worked under the previous version.
A data format is said to be backward compatible with its predecessor if every message or file that is valid under the old format is still valid, retaining its meaning under the new format.
Quadraphonic sound – equivalent to what is now called 4.0 surround sound – uses four channels in which speakers are positioned at the four corners of the listening space, reproducing signals that are independent of one another. Quadraphonic audio was the earliest consumer product in surround sound and thousands of quadraphonic recordings were made during the 1970s.
A subcarrier is a sideband of a radio frequency carrier wave, which is modulated to send additional information. Examples include the provision of colour in a black and white television system or the provision of stereo in a monophonic radio broadcast. There is no physical difference between a carrier and a subcarrier; the "sub" implies that it has been derived from a carrier, which has been amplitude modulated by a steady signal and has a constant frequency relation to it.
C-QUAM is the method of AM stereo broadcasting used in Canada, the United States and most other countries. It was invented in 1977 by Norman Parker, Francis Hilbert, and Yoshio Sakaie, and published in an IEEE journal.
Monaural or monophonic sound reproduction is sound intended to be heard as if it were emanating from one position. This contrasts with stereophonic sound or stereo, which uses two separate audio channels to reproduce sound from two microphones on the right and left side, which is reproduced with two separate loudspeakers to give a sense of the direction of sound sources. In mono, only one loudspeaker is necessary, but, when played through multiple loudspeakers or headphones, identical signals are fed to each speaker, resulting in the perception of one-channel sound "imaging" in one sonic space between the speakers. Monaural recordings, like stereo ones, typically use multiple microphones fed into multiple channels on a recording console, but each channel is "panned" to the center. In the final stage, the various center-panned signal paths are usually mixed down to two identical tracks, which, because they are identical, are perceived upon playback as representing a single unified signal at a single place in the soundstage. In some cases, multitrack sources are mixed to a one-track tape, thus becoming one signal. In the mastering stage, particularly in the days of mono records, the one- or two-track mono master tape was then transferred to a one-track lathe intended to be used in the pressing of a monophonic record. Today, however, monaural recordings are usually mastered to be played on stereo and multi-track formats, yet retain their center-panned mono soundstage characteristics.
Near Instantaneous Companded Audio Multiplex (NICAM) is an early form of lossy compression for digital audio. It was originally developed in the early 1970s for point-to-point links within broadcasting networks. In the 1980s, broadcasters began to use NICAM compression for transmissions of stereo TV sound to the public.
AM stereo is a term given to a series of mutually incompatible techniques for radio broadcasting stereo audio in the AM band in a manner that is compatible with standard AM receivers. There are two main classes of systems: independent sideband (ISB) systems, promoted principally by American broadcast engineer Leonard R. Kahn; and quadrature amplitude modulation (QAM) multiplexing systems.
Matrix decoding is an audio technology where a small number of discrete audio channels are decoded into a larger number of channels on play back. The channels are generally, but not always, arranged for transmission or recording by an encoder, and decoded for playback by a decoder. The function is to allow multichannel audio, such as quadraphonic sound or surround sound to be encoded in a stereo signal, and thus played back as stereo on stereo equipment, and as surround on surround equipment – this is "compatible" multichannel audio.
FM broadcasting is a method of radio broadcasting using frequency modulation (FM) technology. Invented in 1933 by American engineer Edwin Armstrong, wide-band FM is used worldwide to provide high-fidelity sound over broadcast radio. FM broadcasting is capable of better sound quality than AM broadcasting, the chief competing radio broadcasting technology, so it is used for most music broadcasts. Theoretically wideband AM can offer equally good sound quality, provided the reception conditions are ideal. FM radio stations use the VHF frequencies. The term "FM band" describes the frequency band in a given country which is dedicated to FM broadcasting.
Zweikanalton or A2 Stereo, is an analog television sound transmission system used in Germany, Austria, Australia, Switzerland, Netherlands and other countries that use or used PAL-B or PAL-G. South Korea formerly utilised its variant of this format in analogue television system until 31 December 2012. It relies on two separate FM carriers.
In computing, legacy mode is a state in which a computer system, component, or software application behaves in a way different from its standard operation in order to support older software, data, or expected behavior. It differs from backward compatibility in that an item in legacy mode will often sacrifice newer features or performance, or be unable to access data or run programs it normally could, in order to provide continued access to older data or functionality. Sometimes it can allow newer technologies that replaced the old to emulate them when running older operating systems.
MPEG Surround, also known as Spatial Audio Coding (SAC) is a lossy compression format for surround sound that provides a method for extending mono or stereo audio services to multi-channel audio in a backwards compatible fashion. The total bit rates used for the core and the MPEG Surround data are typically only slightly higher than the bit rates used for coding of the core. MPEG Surround adds a side-information stream to the core bit stream, containing spatial image data. Legacy stereo playback systems will ignore this side-information while players supporting MPEG Surround decoding will output the reconstructed multi-channel audio.
In the history of video games, the seventh generation of home consoles began in late 2005 with the release of Microsoft's Xbox 360, and continued with the release of Sony Computer Entertainment's PlayStation 3 (PS3) and Nintendo's Wii the following year. Each new console introduced a new type of breakthrough in technology: the Xbox 360 could play games rendered natively at high-definition video (HD) resolutions; the PlayStation 3 offered HD movie playback via a built-in 3D Blu-ray Disc player; while the Wii focused on integrating controllers with movement sensors as well as joysticks. Some Wii controllers could be moved about to control in-game actions, which enabled players to simulate real-world actions through movement during gameplay. By this generation, video game consoles had become an important part of the global IT infrastructure; it is estimated that video game consoles represented 25% of the world's general-purpose computational power in 2007.
SQ Quadraphonic was a matrix 4-channel quadraphonic sound system for vinyl LP records. It was introduced by CBS Records in 1971. Many recordings using this technology were released on LP during the 1970s.
In the history of video games, the eighth generation of consoles is the current generation. It includes those consoles released since 2012 by Nintendo, Microsoft, and Sony. For home video game consoles, the eighth generation began on November 18, 2012, with the release of the Wii U, and continued with the release of the PlayStation 4 on November 15, 2013, and the Xbox One on November 22, 2013. The Wii U was the first to be discontinued — on January 31, 2017 — to make way for Nintendo's second competitor, the Switch, released on March 3, 2017. These video game consoles follow their seventh generation predecessors from the same three companies: Nintendo's Wii, Sony's PlayStation 3, and Microsoft's Xbox 360.
Various accessories for the PlayStation 2 video game console have been produced by Sony, as well as third parties. These include controllers, audio and video input devices like microphones and video cameras, and cables for better sound and picture quality.
Compatible Discrete 4, also known as Quadradisc or CD-4 was as a discrete four-channel quadraphonic system for phonograph records. The system was created by JVC and RCA in 1971 and introduced in May 1972. Many recordings using this technology were released on LP during the 1970s.