![Wii-gamecube-compatibility](https://upload.wikimedia.org/wikipedia/commons/c/c8/Wii-gamecube-compatibility.jpg)
Backward compatibility (sometimes known as backwards compatibility) is a property of an
operating system
An operating system (OS) is system software that manages computer hardware, software resources, and provides common services for computer programs.
Time-sharing operating systems schedule tasks for efficient use of the system and may also in ...
, product, or
technology
Technology is the application of knowledge to reach practical goals in a specifiable and reproducible way. The word ''technology'' may also mean the product of such an endeavor. The use of technology is widely prevalent in medicine, science, ...
that allows for
interoperability
Interoperability is a characteristic of a product or system to work with other products or systems. While the term was initially defined for information technology or systems engineering services to allow for information exchange, a broader defi ...
with an older
legacy system
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system is an old method, technology, computer system, or application program, "of, relating to, or being a previous or outdated computer system", yet still in use.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 ...
, or with
input designed for such a system, especially in
telecommunications
Telecommunication is the transmission of information by various types of technologies over wire, radio, optical, or other electromagnetic systems. It has its origin in the desire of humans for communication over a distance greater than that fe ...
and
computing
Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes the study and experimentation of algorithmic processes, and development of both hardware and software. Computing has scientific, e ...
.
Modifying a system in a way that does not allow backward compatibility is sometimes called "
breaking" backward compatibility.
A complementary concept is
forward compatibility
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, d ...
. A design that is forward-compatible usually has a
roadmap
A roadmap may refer to:
*A road map, a form of map that details roads and transport links
*A plan, e.g.
**Road map for peace, to resolve the Israeli-Palestinian conflict
**Technology roadmap
A technology roadmap is a flexible planning schedule ...
for compatibility with future standards and products.
A related term from
programming jargon is hysterical reasons or hysterical raisins (near-homophones for "historical reasons"), as the purpose of some software features may be solely to support older hardware or software versions.
Usage
In hardware
A simple example of both backward and forward compatibility is the introduction of
FM radio
FM broadcasting is a method of radio broadcasting using frequency modulation (FM). 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 cap ...
in
stereo
Stereophonic sound, or more commonly stereo, is a method of sound reproduction that recreates a multi-directional, 3-dimensional audible perspective. This is usually achieved by using two independent audio channels through a configuration ...
. FM radio was initially
mono
Mono may refer to:
Common meanings
* Infectious mononucleosis, "the kissing disease"
* Monaural, monophonic sound reproduction, often shortened to mono
* Mono-, a numerical prefix representing anything single
Music Performers
* Mono (Japanese b ...
, with only one audio channel represented by one
signal
In signal processing, a signal is a function that conveys information about a phenomenon. Any quantity that can vary over space or time can be used as a signal to share messages between observers. The ''IEEE Transactions on Signal Processing'' ...
. With the introduction of two-channel stereo FM radio, many listeners had only mono FM receivers. Forward compatibility for mono receivers with stereo signals was achieved by 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
In computer science, an instruction set architecture (ISA), also called computer architecture, is an abstract model of a computer. A device that executes instructions described by that ISA, such as a central processing unit (CPU), is called an ' ...
architectures, one of the most successful being the
x86
x86 (also known as 80x86 or the 8086 family) is a family of complex instruction set computer (CISC) instruction set architectures initially developed by Intel based on the Intel 8086 microprocessor and its 8088 variant. The 8086 was introd ...
family of
microprocessor
A microprocessor is a computer processor where the data processing logic and control is included on a single integrated circuit, or a small number of integrated circuits. The microprocessor contains the arithmetic, logic, and control circu ...
s. Their full backward compatibility spans back to the 16-bit
Intel 8086
The 8086 (also called iAPX 86) is a 16-bit microprocessor chip designed by Intel between early 1976 and June 8, 1978, when it was released. The Intel 8088, released July 1, 1979, is a slightly modified chip with an external 8-bit data bus (allowi ...
/
8088
The Intel 8088 ("''eighty-eighty-eight''", also called iAPX 88) microprocessor is a variant of the Intel 8086. Introduced on June 1, 1979, the 8088 has an eight-bit external data bus instead of the 16-bit bus of the 8086. The 16-bit registers and ...
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
The Intel 8080 (''"eighty-eighty"'') is the second 8-bit microprocessor designed and manufactured by Intel. It first appeared in April 1974 and is an extended and enhanced variant of the earlier 8008 design, although without binary compatibil ...
processor as of 1974. The
Zilog Z80
The Z80 is an 8-bit microprocessor introduced by Zilog as the startup company's first product. The Z80 was conceived by Federico Faggin in late 1974 and developed by him and his 11 employees starting in early 1975. The first working samples wer ...
, however, was fully backward compatible with the Intel 8080.)
Fully backward 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
Application may refer to:
Mathematics and computing
* Application software, computer software designed to help the user to perform specific tasks
** Application layer, an abstraction layer that specifies protocols and interface methods used in a c ...
or
operating system
An operating system (OS) is system software that manages computer hardware, software resources, and provides common services for computer programs.
Time-sharing operating systems schedule tasks for efficient use of the system and may also in ...
s. Similarly, the success of the
Wi-Fi
Wi-Fi () is a family of wireless network protocols, based on the IEEE 802.11 family of standards, which are commonly used for local area networking of devices and Internet access, allowing nearby digital devices to exchange data by radio wave ...
digital communication standard is attributed to its broad forward and backward compatibility; it became more popular than other standards that were not backward compatible.
In software
Compiler
In computing, a compiler is a computer program that translates computer code written in one programming language (the ''source'' language) into another language (the ''target'' language). The name "compiler" is primarily used for programs that ...
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.
Tradeoffs
Benefits
There are several incentives for a company to implement backward compatibility. Backward compatibility can be used to preserve older software that would have otherwise been lost when a manufacturer decides to stop supporting older hardware. Classic video games are a common example used when discussing the value of supporting older software. The cultural impact of video games is a large part of their continued success, and some believe ignoring backward compatibility would cause these titles to disappear. Backward compatibility also acts as a selling point for new hardware, as an existing player base can more affordably
upgrade
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 ...
to subsequent generations of a console. This also helps to make up for lack of content at the launch of new systems, as users can pull from the previous console's library of games while developers transition to the new hardware.
Moreover, studies in the mid-1990s found that even consumers who never play older games after purchasing a new system consider backward compatibility a highly desirable feature, valuing the mere ability to continue to play an existing collection of games even if they choose never to do so.
Backward compatibility with the original
PlayStation
is a video gaming brand that consists of five home video game consoles, two handhelds, a media center, and a smartphone, as well as an online service and multiple magazines. The brand is produced by Sony Interactive Entertainment, a divisi ...
(PS) is considered to have been a key selling point for the
PlayStation 2
The PlayStation 2 (PS2) is a home video game console developed and marketed by Sony Computer Entertainment. It was first released in Japan on 4 March 2000, in North America on 26 October 2000, in Europe on 24 November 2000, and in Australia on 3 ...
(PS2) during its early months on the market.
Despite not being included at launch, Microsoft slowly incorporated backward compatibility for select titles on the Xbox One several years into its product life cycle.
Players have racked up over a billion hours with backward compatible games on Xbox, and the newest generation of consoles such as
PlayStation 5
The PlayStation 5 (PS5) is a home video game console developed by Sony Interactive Entertainment. Announced as the successor to the PlayStation 4 in April 2019, it was launched on November 12, 2020, in Australia, Japan, New Zealand, North Ame ...
and
Xbox Series X/S
The Xbox Series X/S are home video game consoles developed by Microsoft. They were both released on November 10, 2020, as the fourth generation Xbox, succeeding the Xbox One. Along with Sony's PlayStation 5, also released in November 2020, t ...
also support this feature. A large part of the success and implementation of this feature is that the hardware within newer generation consoles is both powerful and similar enough to legacy systems that older titles can be broken down and re-configured to run on the Xbox One.
This program has proven incredibly popular with Xbox players and goes against the recent trend of studio made remasters of classic titles, creating what some believe to be an important shift in console maker's strategies.
Costs
The monetary costs of supporting old software is considered a large drawback to the usage of backward compatibility.
[ The associated costs of backward compatibility are a larger ]bill of materials
A bill of materials or product structure (sometimes bill of material, BOM or associated list) is a list of the raw materials, sub-assemblies, intermediate assemblies, sub-components, parts, and the quantities of each needed to manufacture an end ...
if hardware is required to support the legacy systems; increased complexity of the product that may lead to longer time to market
In commerce, time to market (TTM) is the length of time it takes from a product being conceived until its being available for sale. The reason that time to market is so important is since being late erodes the addressable market into which prod ...
, technological hindrances, and slowing innovation; and increased expectations from users in terms of compatibility. Because of this, several console manufacturers phased out backward compatibility toward the end of the console generation in order to reduce cost and briefly reinvigorate sales before the arrival of newer hardware.
It is possible to bypass some of the hardware costs. In earlier versions of the PS2, a CPU core identical to that of the PS serves a dual purpose, either as the main CPU in PS mode, or upclocking itself to offload I/O in PS2 mode. Such an approach can backfire, however, as in the case of the Super Nintendo Entertainment System
The Super Nintendo Entertainment System (SNES), commonly shortened to Super NES or Super Nintendo, is a 16-bit home video game console developed by Nintendo that was released in 1990 in Japan and South Korea, 1991 in North America, 1992 in Eur ...
(Super NES), which opted for the peculiar 65C816
The W65C816S (also 65C816 or 65816) is an 8/16-bit microprocessor (MPU) developed and sold by the Western Design Center (WDC). Introduced in 1985, the W65C816S is an enhanced version of the WDC 65C02 8-bit MPU, itself a CMOS enhancement of the ve ...
over more popular 16-bit microprocessors on the basis that it would allow easy compatibility with the original NES
The Nintendo Entertainment System (NES) is an 8-bit third-generation home video game console produced by Nintendo. It was first released in Japan in 1983 as the commonly known as the The NES, a redesigned version, was released in American ...
, but NES compatibility ultimately did not prove workable once the rest of the Super NES's architecture was designed.
Backward compatibility introduces the risk that developers will favor developing games that are compatible with both the old and new systems, since this gives them a larger base of potential buyers, resulting in a dearth of software which uses the advanced features of the new system.[
With the decline in physical game sales and the rise of digital storefronts and downloads, some believe backward compatibility will soon be obsolete.] Many game studios are re-mastering and re-releasing their most popular titles by improving the quality of graphics and adding new content. These remasters have found success by appealing both to nostalgic players who remember enjoying the original versions, and to newcomers who may not have had the original system it was released on. For most consumers, digital remasters are more appealing than hanging on to obsolete hardware. For the manufacturers of consoles, digital re-releases of classic titles are a large benefit. It not only removes the financial drawbacks of supporting older hardware, but also shifts all of the costs of updating software to the developers. The manufacturer gets a new addition to their system with name recognition, and the studio does not have to develop a new game.
See also
References
External links
* {{Commons category-inline
Interoperability