Editing Porting

{{Short description|Process of adapting software to run in other computing environments}}
In [[software engineering]], '''porting''' is the process of adapting [[software]] for the purpose of achieving some form of execution in a [[Computing platform|computing environment]] that is different from the one that a given program (meant for such execution) was originally designed for (e.g., different [[Central processing unit|CPU]], operating system, or third party [[Library (computer science)|library]]). The term is also used when software/hardware is changed to make them usable in different environments.<ref>{{cite journal |date=March 1975
|title=A machine and configuration independent Fortran: Portable Fortran
|first1=D.E. |last1=Whitten |first2=P.A.D. |last2=Demaine |journal=IEEE Transactions on Software Engineering |volume=SE-1 |issue=1 |pages=111–124 |doi=10.1109/TSE.1975.6312825|s2cid=16485156}}</ref><ref>{{cite web |title=Portability Issues
|url=https://www.gnu.org/software/sather/docs-1.2/tutorial/fortran-portability.html
|quote=.. discusses .. portability of .. Fortran}}</ref>

Software is [[Software portability|''portable'']] when the cost of porting it to a new platform is significantly less than the cost of writing it from scratch. The lower the cost of porting software relative to its implementation cost, the more portable it is said to be. This is distinct from [[cross-platform software]], which is designed from the ground up without any single "[[Native_(computing)|native]]" platform.

== Etymology ==
The term "port" is derived from the Latin ''[[wikt:port#Etymology 3|portāre]]'', meaning "to carry".<ref>{{Cite web|url=http://www.oed.com/view/Entry/148098|title=port, v.2|website=Oxford English Dictionary (OED Online)|publisher=Oxford University Press|access-date=December 21, 2017|url-access=subscription |quote=Origin: Of multiple origins. Partly a borrowing from French. Partly a borrowing from Latin. Etymons: French ''porter''; Latin ''portāre''. ...  1. ''trans.'' To carry, bear, or convey; to bring.}}</ref> When code is not compatible with a particular [[operating system]] or [[Computer architecture|architecture]], the code must be "carried" to the new system.

The term is not generally applied to the process of adapting software to run with less memory on the same CPU and operating system.

Software developers often claim that the software they write is ''[[Portability (software)|portable]]'', meaning that little effort is needed to adapt it to a new environment. The amount of effort actually needed depends on several factors, including the extent to which the original environment (the ''source platform'') differs from the new environment (the ''target platform''), the experience of the original authors in knowing which [[programming language]] constructs and third party library calls are unlikely to be portable, and the amount of effort invested by the original authors in only using portable constructs (platform specific constructs often provide a cheaper solution).

== History ==
The number of significantly different CPUs and operating systems used on the desktop today is much smaller than in the past. The dominance of the [[x86]] [[instruction set|architecture]] means that most desktop software is never ported to a different CPU. In that same market, the choice of operating systems has effectively been reduced to three: [[Microsoft Windows]], [[macOS]], and [[Linux]]. However, in the [[embedded systems]] and [[mobile computing|mobile]] markets, [[Portability (software)|portability]] remains a significant issue, with the [[ARM architecture|ARM]] being a widely used alternative.

International standards, such as those promulgated by the [[International Organization for Standardization|ISO]], greatly facilitate porting by specifying details of the computing environment in a way that helps reduce differences between different standards-conforming [[platform (computing)|platforms]]. Writing software that stays within the bounds specified by these standards represents a practical although nontrivial effort. Porting such a program between two standards-compliant platforms (such as [[POSIX|POSIX.1]]) can be just a matter of loading the source code and [[compiling|recompiling]] it on the new platform, but practitioners often find that various minor corrections are required, due to subtle platform differences. Most standards suffer from "gray areas" where differences in interpretation of standards lead to small variations from platform to platform.

There also exists an ever-increasing number of tools to facilitate porting, such as the [[GNU Compiler Collection]], which provides consistent programming languages on different platforms, and [[Autotools]], which automates the detection of minor variations in the environment and adapts the software accordingly before compilation.

The compilers for some [[high-level programming language]]s (e.g. [[Eiffel (programming language)|Eiffel]], [[Esterel]]) gain portability by outputting source code in another high level [[intermediate language]] (such as [[C (programming language)|C]]) for which compilers for many platforms are generally available.

Two activities related to (but distinct from) porting are [[emulator|emulating]] and [[cross-compiling]].

==Porting compilers==
Instead of translating directly into [[machine code]], modern [[compilers]] translate to a machine independent [[intermediate code]] in order to enhance portability of the compiler and minimize design efforts. The intermediate language defines a ''[[virtual machine]]'' that can execute all programs written in the [[intermediate language]] (a&nbsp;machine is defined by its language and vice versa).<ref name="Machinelanguage">{{harvnb|Tanenbaum|1984|p=3|loc=§&nbsp;1.1 Languages, Levels, and Virtual Machines}} describes the terms and their relations.</ref> The intermediate code instructions are translated into equivalent machine code sequences by a ''code generator'' to create [[executable code]]. It is also possible to skip the generation of machine code by actually implementing an [[interpreter (computing)|interpreter]] or [[Just in time compiler|JIT]] for the virtual machine.<ref>{{harvnb|Tanenbaum|1984|p=2. Ch. 1 Introduction}} explains translation and interpretation.</ref>

The use of intermediate code enhances portability of the compiler, because only the machine dependent code (the interpreter or the code generator) of the compiler itself needs to be ported to the target machine. The remainder of the compiler can be imported as intermediate code and then further processed by the ported code generator or interpreter, thus producing the compiler software or directly executing the intermediate code on the interpreter. The machine independent part can be developed and [[software testing|tested]] on another machine (the ''host machine''). This greatly reduces design efforts, because the machine independent part needs to be developed only once to create portable intermediate code.<ref>{{harvnb|Richards|Whitby-Strevens|1984|p=124|loc=§&nbsp;7.1 Introduction}} explains compiler portability using intermediate code.</ref>

An interpreter is less complex and therefore easier to port than a code generator, because it is not able to do code optimizations due to its limited view of the program code (it only sees one instruction at a time, and users need a sequence to do optimization). Some interpreters are extremely easy to port, because they only make minimal assumptions about the instruction set of the underlying hardware. As a result, the virtual machine is even simpler than the target CPU.<ref>{{harvnb|Richards|Whitby-Strevens|1984|p=133|loc=§&nbsp;7.4 The bootstrapping process and INTCODE}} explains the role of the INTCODE interpreter.</ref>

Writing the compiler sources entirely in the programming language the compiler is supposed to translate, makes the following approach, better known as ''[[Bootstrapping (compilers)|compiler bootstrapping]]'', feasible on the target machine: 
# Port the interpreter. This needs to be coded in [[assembly code]], using an already present [[Assembly language|assembler]] on the target.
# Adapt the source of the code generator to the new machine.
# Execute the adapted source using the interpreter with the code generator source as input. This will generate the machine code for the code generator.

The difficult part of coding the optimization routines is done using the high-level language instead of the assembly language of the target.

According to the designers of the [[BCPL]] language, interpreted code (in the BCPL case) is more compact than machine code, typically by a factor of two to one. Interpreted code however runs about ten times slower than compiled code on the same machine.<ref>{{harvnb|Richards|Whitby-Strevens|1984|p=136|loc=§&nbsp;7.4.3 Example}} gives an example translation of a BCPL program into INTCODE for the interpreter.</ref>

The designers of the [[Java (programming language)|Java programming language]] try to take advantage of the compactness of interpreted code, because a Java program may need to be transmitted over the Internet before execution can start on the target's [[Java virtual machine]] (JVM).

== {{Anchor|Porting in gaming|conversion}} Porting of video games ==
{{Redirect|Video game port|the hardware connector|Game port}}
Porting is also the term used when a [[video game]] designed to run on one platform, be it an [[Arcade game|arcade]], [[video game console]], or [[personal computer]], is converted to run on a different platform, perhaps with some minor differences.<ref name="Wolf2008">{{cite book|last=Wolf|first=Mark J. P.|title=The Video Game Explosion: A History from PONG to Playstation and Beyond|chapter-url=https://books.google.com/books?id=XiM0ntMybNwC&pg=PA315|year=2008|isbn=978-0-313-33868-7|page=315|chapter=Glossary|publisher=Bloomsbury Academic}}</ref> From the beginning of video games through to the 1990s, "ports", at the time often known as "[[Video game conversion|conversions]]", were often not true ports, but rather reworked versions of the games due to the limitations of different systems. For example, the 1982 game ''[[The Hobbit (1982 video game)|The Hobbit]]'', a text adventure augmented with graphic images, has significantly different graphic styles across the range of personal computers that its ports were developed for.<ref name="port vs conversion">{{citation | last1 = Grabarczyk | first1 = Pawel | first2 = Espen | last2= Aarseth | title = Port or conversion? An ontological framework for classifying game versions {{!}} DiGRA Conference 2019 | date = 2019}}</ref> However, many 21st century video games are developed using software (often in [[C++]]) that can output code for one or more consoles as well as for a PC without the need for actual porting (instead relying on the common porting of individual component [[Library (software)|libraries]]).<ref name="port vs conversion"/>

Porting arcade games to home systems with inferior hardware was difficult. The ported version of ''[[Pac-Man]]'' for the [[Atari 2600]] omitted many of the visual features of the original game to compensate for the lack of [[ROM]] space and the hardware struggled when multiple ghosts appeared on the screen creating a flickering effect. The poor performance of the [[Pac-Man (Atari 2600)|Atari 2600 ''Pac-Man'']] is cited by some scholars as a cause of the [[video game crash of 1983]].<ref>{{cite journal |last1=Nicoll |first1=Benjamin |title=Bridging the Gap: The Neo Geo, the Media Imaginary, and the Domestication of Arcade Games |journal=Games and Culture |date=2015 |doi=10.1177/1555412015590048|s2cid=147981978}}</ref>

Many early ports suffered significant gameplay quality issues because computers greatly differed.{{r|bunten198412}} [[Richard Garriott]] stated in 1984 at [[Origins Game Fair]] that [[Origin Systems]] developed video games for the [[Apple II]] first then ported them to [[Commodore 64]] and [[Atari 8-bit computers]], because the latter machines' [[sprite (computer graphics)|sprite]]s and other sophisticated features made porting from them to Apple "far more difficult, perhaps even impossible".<ref name="cgw198410">{{cite magazine | title=The CGW Computer Game Conference | magazine=Computer Gaming World | date=October 1984 | access-date=31 October 2013 | url=http://www.cgwmuseum.org/galleries/index.php?year=1984&pub=2&id=18 | pages=30 | type=panel discussion}}</ref> Reviews complained of ports that suffered from "Apple conversionitis",<ref name="info198701c64">{{Cite magazine |last1=Dunnington |first1=Benn |last2=Brown |first2=Mark R. |last3=Malcolm |first3=Tom |date=January–February 1987 |title=64/128 Gallery |url=https://archive.org/stream/info-magazine-13/Info_Issue_13_1987_Jan-Feb#page/n13/mode/2up |magazine=Info |pages=14–21}}</ref> retaining the Apple's "lousy sound and black-white-green-purple graphics";<ref name="aw1984">{{cite book | url=https://archive.org/stream/Atari_Software_1984#page/n21/mode/2up | title=The Addison-Wesley Book of Atari Software | publisher=Addison-Wesley | year=1984 | pages=12,21,44,126 | isbn=0-201-16454-X | editor1=Stanton, Jeffrey | editor2=Wells, Robert P. | editor3=Rochowansky, Sandra | editor4=Mellid, Michael}}</ref><ref name="bernstein198505">{{cite news | url=https://archive.org/stream/1985-05-anticmagazine/Antic_Vol_4-01_1985-05_New_Super_Ataris#page/n81/mode/2up | title=Beyond Castle Wolfenstein | work=Antic | date=May 1985 | access-date=8 January 2015 | author=Bernstein, Harvey | pages=83}}</ref> after Garriott's statement, when [[Dan Bunten]] asked "Atari and Commodore people in the audience, are you happy with the Apple rewrites?" the audience shouted "No!" Garriott responded, "[otherwise] the Apple version will never get done. From a publisher's point of view that's not money wise".{{r|cgw198410}}

Others worked differently. [[Ozark Softscape]], for example, wrote ''[[M.U.L.E.]]'' for the Atari first because it preferred to develop for the most advanced computers, removing or altering features as necessary during porting. Such a policy was not always feasible; Bunten stated that "M.U.L.E. can't be done for an Apple",<ref name="bunten198412">{{cite magazine | title=Dispatches / Insights From the Strategy Game Design Front | magazine=Computer Gaming World | url=http://www.cgwmuseum.org/galleries/index.php?year=1984&pub=2&id=19 | date=December 1984 | access-date=31 October 2013 | author=Bunten, Dan | pages=40}}</ref> and that the non-Atari versions of ''[[The Seven Cities of Gold (video game)|The Seven Cities of Gold]]'' were inferior.<ref name="buntengamedesignmemoir">{{Cite web |url=http://www.ozarksoftscape.com/the-game-collection.html |title=The Game Collection |last=Bunten |first=Dan |website=Ozark Softscape M.U.L.E. |access-date=2017-10-04}}</ref> ''[[Compute!'s Gazette]]'' wrote in 1986 that when porting from Atari to Commodore the original was usually superior. The latter's games' quality improved when developers began creating new software for it in late 1983, the magazine stated.<ref name="Yakal198606">{{Cite magazine |last=Yakal |first=Kathy |date=June 1986 |title=The Evolution of Commodore Graphics |url=https://archive.org/details/1986-06-computegazette/page/n35 |magazine=Compute!'s Gazette |pages=34–42 |access-date=2019-06-18}}</ref>

In porting [[arcade game]]s, the terms "arcade perfect" or "arcade accurate" were often used to describe how closely the gameplay, graphics, and other assets on the ported version matched the arcade version. Many arcade ports in the early 1980s were far from arcade perfect as home consoles and computers lacked the sophisticated hardware in arcade games, but games could still approximate the gameplay. Notably, ''[[Space Invaders]]'' on the [[Atari VCS]] became the console's [[killer app]] despite its differences,<ref>{{cite book |title=[[Ultimate History of Video Games]] |first=Steven |last=Kent | authorlink = Steven L. Kent |page=190 |publisher=[[Three Rivers Press]] |isbn=0-7615-3643-4 |year=2001}}</ref> while the later [[Pac-Man (Atari 2600)|''Pac-Man'' port]] was notorious for its deviations from the arcade version.<ref>{{cite book | title = The Ultimate History of Video Games | last = Kent | first = Steven | year = 2001 | chapter = The Fall | publisher = [[Three Rivers Press]] | pages = 237–239 | isbn = 978-0-7615-3643-7}}</ref> Arcade-accurate games became more prevalent starting in the 1990s as home consoles caught up to the power of arcade systems. Notably, the [[Neo Geo (system)|Neo Geo]] system from [[SNK]], which was introduced as a multi-game arcade system, would also be offered as a home console with the same specifications. This allowed arcade perfect games to be played at home.<ref name="port vs conversion"/>

A "console port" is a game that was originally or primarily made for a console before a version is created which can be played on a [[personal computer]]. The process of porting games from console to PC is often regarded more cynically than other types of port due to the more powerful hardware some PCs have even at console launch being underutilized, partially due to console hardware being fixed throughout each [[History of video game consoles#Console generations|generation]] as newer PCs constantly become even more powerful. While broadly similar today, some architectural differences persist, such as the use of [[unified memory]] and smaller [[Operating system|OSs]] on consoles. Other objections arise from [[user interface]] differences conventional to consoles, such as [[gamepad]]s, [[10-foot user interface|TFUIs]] accompanied by narrow [[Field of view in video games|FoV]], fixed [[Saved game#Checkpoints|checkpoints]], [[Online game|online]] restricted to official [[Game server|servers]] or [[Peer-to-peer|P2P]], poor or no [[Video game modding|modding]] support, as well as the generally greater reliance among console developers on internal [[hard coding]] and [[Default (computer science)|defaults]] instead of external [[API]]s and [[Computer configuration|configurability]], all of which may require expensive deep reaching redesign to avoid a "lazy" feeling port to PC.<ref>{{cite web |url=https://www.pcgamer.com/stop-making-horrible-console-ports-a-guide/ |title=Stop making horrible console ports - a guide |publisher=[[PC Gamer]] |year=2013}}</ref>

==See also==
* [[Software portability]]
* [[Cross-platform software]]
* [[Write once, compile anywhere]]
* [[Program transformation]]
* [[List of system quality attributes]]
* [[Language binding]]
* [[Source-to-source compiler]]
* [[Console emulator]]
* [[Source port]]
* [[Poshlib]]
* [[wikt:unported|Meaning of ''unported'']]

==References==
{{Reflist}}
* {{cite book |author-link=Martin Richards (computer scientist) |first1=Martin |last1=Richards |first2=Colin |last2=Whitby-Strevens |title=BCPL, the language and its compiler |year=1984 |publisher=Cambridge University Press |isbn=0-521-28681-6}}
* {{cite book |author-link=Andrew S. Tanenbaum |first=Andrew S. |last=Tanenbaum |title=Structured computer organization |year=1984 |publisher=Prentice-Hall |isbn=0-13-854605-3}}

[[Category:Interoperability]]
[[Category:Source code]]

[[de:Portierung]]