Software component that extends the functionality of existing software From Wikipedia, the free encyclopedia
In computing, a plug-in (or plugin, add-in, addin, add-on, or addon) is a software component that extends the functionality of an existing software system without requiring the system to be re-built. A plug-in feature is one way that a system can be customizable.[1]
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Applications support plug-ins for a variety of reasons including:
Examples of plug-in use for various categories of applications:
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 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.[11][12]
Programmers typically implement plug-ins as shared libraries, which get 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 files written in a scripting language like Python or Lua.
In the context of a web browser, a helper application is a separate program—like IrfanView or Adobe Reader—that extends the functionality of a browser.[13][14] 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.[15]
In the mid-1970s, the 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.[16] 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.
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