X Window System

A window system for computers with bitmap graphical displays. Created at MIT in the 1980s, it is now under the supervision of the X Consortium (http://www.x.org/). Currently at version 11, release 6 (X11R6), the X Window System is more commonly called X11 or simply X. It is also often referred to as "X Windows", analogous to "Microsoft Windows", but this usage is incorrect and discouraged.

Although X provides functionality for drawing and moving Windows on the screen and also for providing a mouse cursor it provides none of the user interface features (such as buttons, menus, window title bars and so on) that people expect. These features are provided by other pieces of software, such as window managers, graphics toolkits, and the like.

Several different desktop environments have been developed to provide consistency and improved services for X Window applications. Motif? and Openlook? were the earliest. Motif was later replaced with CDE. KDE and Gnome are the latest additions, providing much greater application functionality and services than just simple window management.

X is based on a client-server model. A server program runs on a computer with a graphical display and communicates with various client programs, accepting requests for graphical output (windows) and sending back user input (keyboard, mouse). The communication protocol between server and client is network?-transparent: the client programs can be run on the same machine as the server or equally well from other machines, possibly with different architectures and operating systems.

The client-server terminology is often confusing to new X users, because the terms are used differently than in other common contexts. In a typical X scenario, a user may be sitting at an X terminal or workstation where they interact with the keyboard and display, while their application program may be running on some big machine locked away in a computer room somewhere. Common terminology would refer to the workstation or terminal as a "client" and the other machine in the computer room as a "server", but the X terminology is different. The X terms are used from the point of view of the application program, not the end user or the hardware. The application program is the client, which needs to use keyboard and display services. Therefore the workstation or terminal software is the X server, and the application program is the X client.

The X Window System is distributed at no charge, with source code and no restrictions on modification and redistribution. Due to the liberal licensing, a number of implementations (both free and proprietary) appeared that were based on the code from MIT. Originally developed for the Unix graphical workstations? of the 1980s as part of MIT's [Project Athena]?, these enhanced versions mainly added compatibility with specific operating systems and hardware. X became a part of the "standard" Unix offerings. Although other windowing systems for Unix exist, X is by far the most common.

While being the standard on Unix, there are also X servers for platforms with their own graphical environments, like Microsoft Windows or MacOS.

The variant most widely used on free Unix-like systems is XFree86, which originally ran only on Intel x86-type PCs (hence the name), but now incorporates support for many more platforms.

X is named after an earlier window system called W (in the modern Roman alphabet the letter X comes right after W).

See also History of the GUI