View source for Plug-in (computing)

{{short description|Software component that extends the functionality of existing software}}
{{More citations needed|date=September 2019}}
[[File:Mozilla plugins screenshot without subpixel rendering.png|thumb|[[Mozilla Firefox]] displaying a list of installed plug-ins]]
{{Wiktionary|plug-in|add-on}}

In [[computing]], a '''plug-in''' (also spelled '''plugin'''), '''add-in''' (also '''addin''', '''add-on''', or '''addon''') or '''extension''' is a [[software component]] that extends the functionality of an existing [[software system]] without requiring the system to be [[software build|re-built]]. A plug-in [[software feature|feature]] is one way that a system can be [[customizable]].<ref>{{Cite web|last=Sterne|first=Jonathan|date=|title=Plug-in {{!}} software|url=https://www.britannica.com/technology/plug-in|access-date=2021-02-05|website=Encyclopedia Britannica|language=en}}</ref>

Applications support plug-ins for a variety of reasons including:
* Enable [[third-party developer]]s to extend an application
* Support easily adding new features
* Reduce the size of an application by not loading unused features
* Separate [[source code]] from an application because of incompatible [[software license]]s

==Examples==

Examples of plug-in use for various categories of applications:

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* [[Digital audio workstation]]s and [[audio editing software]] use [[audio plug-in]]s to generate, process or analyze sound. [[Ardour (software)|Ardour]], [[Audacity (audio editor)|Audacity]], [[Cubase]], [[FL Studio]], [[Logic Pro|Logic Pro X]] and [[Pro Tools]] are examples of such systems.
* [[Email client]]s use plug-ins to decrypt and encrypt email. [[Pretty Good Privacy]] is an example of such plug-ins.
* [[Video game console emulator]]s often use plug-ins to modularize the separate subsystems of the devices they seek to emulate.<ref>{{Cite web|url=https://pcsx2.net/download/category/41-win-plugins.html|title=PCSX2 - The Playstation 2 emulator - Plugins|website=pcsx2.net|language=en-gb|access-date=2018-06-10|archive-date=2018-01-25|archive-url=https://web.archive.org/web/20180125215009/https://pcsx2.net/download/category/41-win-plugins.html|url-status=dead}}</ref><ref>{{Cite web|url=http://www.pbernert.com/html/gpu.htm|title=Pete's PSX GPU plugins|last=Bernert|first=Pete|website=www.pbernert.com|access-date=2018-06-10}}</ref><ref>{{Cite web|url=http://demul.emulation64.com/downloads/|title=DEMUL - Sega Dreamcast Emulator for Windows|last=Team|first=Demul|website=demul.emulation64.com|access-date=2018-06-10}}</ref><ref>{{Cite web|url=https://wiki.jenkins.io/display/JENKINS/Android+Emulator+Plugin|title=Android Emulator Plugin - Jenkins - Jenkins Wiki|website=wiki.jenkins.io|access-date=2018-06-10}}</ref><ref>{{Cite web|url=https://github.com/OpenEmu/SNES9x-Core|title=OpenEmu/SNES9x-Core|website=GitHub|language=en|access-date=2018-06-10}}</ref><ref>{{Cite news|url=http://emulation-general.wikia.com/wiki/Recommended_N64_Plugins|title=Recommended N64 Plugins|work=Emulation General Wiki|access-date=2018-06-10|language=en}}</ref><ref>{{Cite web|url=http://www.emulator-zone.com/doc.php/psx/psxplugins-tools.html|title=Playstation plugins & utilities!|website=www.emulator-zone.com|access-date=2018-06-10}}</ref><ref>{{Cite web|url=http://www.psx-place.com/categories/ps3-homebrew-apps-plugins-emulators.50/|title=PS3 Homebrew Apps / Plugins / Emulators {{!}} PSX-Place|website=www.psx-place.com|language=en-US|access-date=2018-06-10}}</ref>  For example, the [[PCSX2]] emulator makes use of video, audio, optical, etc. plug-ins for those respective components of the [[PlayStation 2]].
* [[Graphics software]] use plug-ins to support file formats and process images. A [[Photoshop plug-in]] may do this.
* Broadcasting and live-streaming software, like [[OBS Studio]], as an open source software utilizes plug-ins for user-specific needs.
* [[Media player (software)|Media players]] use plug-ins to support file formats and apply filters. [[foobar2000]], [[GStreamer]], [[Quintessential Media Player|Quintessential]], [[VLC media player|VLC]], [[Winamp]], and [[XMMS]] are examples of such media players.
* [[Packet sniffer]]s use plug-ins to decode packet formats. [[OmniPeek]] is an example of such packet sniffers.
* [[Remote sensing application]]s use plug-ins to process data from different sensor types; e.g., [[Opticks (Software)|Opticks]].
* [[Text editors]] and [[integrated development environment]]s use plug-ins to support [[programming languages]] or enhance the development process, e.g., [[Microsoft Visual Studio|Visual Studio]], [[RAD Studio]], [[Eclipse (computing)|Eclipse]], [[IntelliJ IDEA]], [[jEdit]] and [[MonoDevelop]] support plug-ins. Visual Studio itself can be plugged into other applications via [[Visual Studio Tools for Office]] and [[Visual Studio Tools for Applications]].
* [[Web browser]]s have historically used [[executable]]s as plug-ins, though they all are [[deprecation|deprecated]]. Examples include the [[Adobe Flash Player]], a [[Java virtual machine]] (for [[Java applets]]), [[QuickTime]], [[Microsoft Silverlight]] and the [[Unity (game engine)#Supported platforms|Unity Web Player]]. ([[Browser extension]]s, which are a separate type of installable module, are still widely in use.)
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==Mechanism==
[[File:Plug-InExample.svg|325px|thumb|right|Example Plug-In Framework]]

The host application provides services which the plug-in can use, including a way for plug-ins to register themselves with the host application and a [[Protocol (computing)|protocol]] for the exchange of data with plug-ins. Plug-ins depend on the services provided by the host application and do not usually work by themselves. Conversely, the host application operates independently of the plug-ins, making it possible for end-users to add and update plug-ins dynamically without needing to make changes to the host application.<ref name="amo-def">[https://addons.mozilla.org/en-US/firefox/browse/type:7 Mozilla Firefox plugins] – Description of the difference between Mozilla Firefox plugins and extensions under the general term ''add-on''.</ref><ref name="wordpress-def">[http://codex.wordpress.org/Plugin_API Wordpress Plug-in API] – Description of the Wordpress Plug-in architecture.</ref>

Programmers typically implement plug-ins as [[Shared library|shared libraries]], which get [[Dynamic loading|dynamically loaded]] at run time. [[HyperCard]] supported a similar facility, but more commonly included the plug-in code in the HyperCard documents (called ''stacks'') themselves. Thus the HyperCard stack became a self-contained application in its own right, distributable as a single entity that end-users could run without the need for additional installation-steps. Programs may also implement plug-ins by loading a directory of simple [[script (computing)|script]] files written in a [[scripting language]] like [[Python (programming language)|Python]] or [[Lua]].

==Helper application==
In the context of a [[web browser]], a helper application is a separate program{{mdash}}like [[IrfanView]] or [[Adobe Reader]]{{mdash}}that extends the functionality of a browser.<ref>{{Cite web |title=Definition of helper application |url=https://www.pcmag.com/encyclopedia/term/helper-application |access-date=2022-10-25 |website=PCMAG |language=en}}</ref><ref>{{cite web |title=Download Irfan using Internet Explorer 4.x or above |url=https://libweb.hawaii.edu//digicoll/ttp/IrfanView/ie4.html |website=libweb.hawaii.edu |access-date=9 January 2024}}</ref> A helper application extends the functionality an application but unlike the typical plug-in that is loaded into the host application's [[address space]], a helper application is a separate application. With a separate address space, the extension cannot crash the host application as is possible if they share an address space.<ref>{{cite web |title=Helper Applications and Plug-ins - Web Security, Privacy & Commerce, 2nd Edition [Book] |url=https://www.oreilly.com/library/view/web-security-privacy/0596000456/ch12s02.html |website=Web Security, Privacy, and Commerce 2nd Edition |publisher=O'Reilly |language=en}}</ref>

==History==
In the mid-1970s, the [[EDT (Univac)|EDT]] [[text editor]] ran on the [[Unisys]] [[VS/9]] [[operating system]] for the [[UNIVAC Series 90]] [[mainframe computer]]. It allowed a program to be run from the editor, which can access the in-memory edit buffer.<ref>''EDT Text Editor Reference Manual'', [[Cinnaminson, New Jersey]]: [[Unisys Corporation]], 1975</ref>  The plug-in executable could call the editor to inspect and change the text. The [[University of Waterloo]] Fortran compiler used this to allow interactive compilation of [[Fortran]] programs.

Early personal computer software with plug-in capability included HyperCard and [[QuarkXPress]] on the [[Apple Macintosh]], both released in 1987. In 1988, [[Silicon Beach Software]] included plug-in capability in [[Digital Darkroom]] and [[SuperPaint (Macintosh)|SuperPaint]].

==See also==
* {{annotated link|Add-on (Mozilla)}}
* {{annotated link|Applet}}
* {{annotated link|Browser extension}}
* {{annotated link|theme (computing)|Theme}}

==References==
{{Reflist}}

{{Authority control}}

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[[Category:Application programming interfaces]]
[[Category:Software add-ons|*]]
[[Category:Technology neologisms]]