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  Wikipedia: X Window System

Wikipedia: X Window System
X Window System
From Wikipedia, the free encyclopedia.

The X Window System is a windowing system for computers with bitmap displays. It is standard on Unix, Linux and other Unix-like operating systems and is available for most other modern operating systems.

X provides basic underpinnings for a graphical user interface (GUI): drawing and moving windowss on a screen and interacting with a mouse cursor. It does not provide the user interface features of a graphical interface (buttonss, menuss, window title bars and so on) — these features are provided by other pieces of software, such as window managers, GUI widget toolkits and desktop environments. Thus, the usual visual interface of X-based environments has changed over the years, and several different interface styles may coexist on one computer.

All X-based programs benefit from X's basic features, the most important of which is network transparency: the machine where an application program runs (the application client) can be separate from the user's local machine (the display server). (X's usage of the terms "client" and "server" is the opposite of what most people expect, because here the "server" is the user's local display instead of the remote machine.)

X originated at MIT in the 1980s. The project is now led by the X.Org Foundation. The current release is version 11 release 6.6 (X11R6.6).


X is based on a client-server model. A display 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 runs network-transparently: the client programs can run on the same machine as the server or on other machines, possibly with different architectures and operating systems.

For example, one could run a large computational simulation on a far-away Unix supercomputer (the "client") while displaying the simulation user interface and results on the user's local desktop machine (the "server", which could be running Windows or any other operating system). Other possibilities include administering a remote machine using graphical software on that machine, using remote application software from thin client machines with little or no processing power or storage, and running graphical software on several machines at once via a single display.

This client-server terminology—your terminal is the "server", the remote application is the "client"—often confuses new X users, because the terms appear reversed from what they might expect. X takes the perspective of the program, rather than the end-user or the hardware: the remote programs connect to the X server display running on the local machine, and thus become X clients; the local X display accepts incoming traffic, and hence acts as a server.

Color modes of the X Window System

The colors used in X Window Systems sometimes confuse users, as old or special-purpose applications may require a certain color mode. Nowadays most applications use a color mode called "TrueColor", but historically X has supported several different modes:

X terminals

An X terminal is a a piece of dedicated hardware running an X server as a thin client. This architecture became popular for building inexpensive client parks for many users to simultaneously use the same large server. This use very much aligns with the original intention of the MIT project.

X terminals explore the available hosts using an ad hoc network protocol called XDMCP to connect to a specific server which presents a list of available hosts. This server in turn may gather a list of available hosts using broadcast on the local network.

Dedicated X terminals are no longer common; this functionality is now typically provided either with a user's Microsoft Windows PC running an X server program or a low-end PC running Linux.

X Display Managers

The X Display Manager keeps the X server process alive on the X server machine, connecting it to a physical screen and serving a login prompt on this screen. XDM serves as the default display manager for X, but other projects have developed their own display managers:

Widget toolkits and desktop environments

Several different widget toolkits, window managers and desktop environments have developed to provide consistency and improved services for X applications. Early GUI toolkits for X included:

OLIT and XView function as the base toolkits for AT&T and Sun's OPEN LOOK GUI.

Motif provides the base toolkit for the Common Desktop Environment (CDE), which is the standard desktop environment used on commercial Unix systems such as Solaris and HP-UX. (GNOME is offered in Solaris 9 and will be standard in future versions.)

GTK+ (the GIMP Toolkit, as used in GNOME) and Qt (as used in KDE) have become the present-day toolkits of choice for open source Unix-like systems. The KDE and GNOME desktop environments provide much better application functionality and services than is offered by plain window managers or older desktop environments.

Distribution model

X.Org distributes the X Window System at no charge, with source code included and no restrictions on modification or redistribution, under the MIT License.

Due to the liberal licensing, a number of implementations (both free and proprietary) have appeared, 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.

Implementations of X

While Unix has standardized on X, X servers also exist for platforms with their own graphical environments, like Windows, Mac OS/MacOS X and OS/2.

Commercial Unix vendors tend to take the reference implementation and adapt it for their hardware, usually customising it heavily and adding proprietary extensions.

The X variant most common on free Unix-like systems, XFree86, originally ran only on Intel x86-type PCs (hence the name), but now incorporates support for many more platforms. A proprietary variant named Accelerated-X is a development on top of the same X386 server included in the X Window System distribution.

X11 servers used on Windows include:

Apple Computer's Mac OS X 10.3 (Panther) release includes Apple's version of X11.


X derives its name as a successor to a pre-1983 window system called W (the letter X directly following W in the Latin alphabet).

The X Window System concept first emerged in 1984, at the Massachusetts Institute of Technology (MIT), as a joint project between their Laboratory for Computer Science and Digital Equipment Corporation. The initial impetus came from MIT's Project Athena, which sought to provide easy access to computing resources for all students. Because MIT could not buy all the workstations needed, and no single vendor appeared willing to donate them, the Institute needed a platform-independent graphics system to link together its heterogeneous systems.

The first version to achieve wide deployment was Version 10 (X10). Version 11 (X11), the present version, superseded it shortly thereafter, in 1987.

In 1988, a non-profit group called the (MIT) X Consortium formed to direct future development of X standards in an atmosphere inclusive of commercial and educational interests. The X Consortium produced several significant revisions to X11, the last being Release 6 in 1994 (X11R6). The Consortium dissolved at the end of 1996, producing a final, small revision called X11R6.3.

Stewardship of X then passed to The Open Group, an outgrowth of the Open Software Foundation (OSF), who produced the popular Motif widget toolkit for X. In early 1998, the Open Group released a further revision to X11R6, called X11R6.4. A departure from the traditional licensing terms, however, inhibited many vendors, including the XFree86 Project, Inc., from adopting this version of the X Window System. As such, the Open Group relicensed X11R6.4 under terms identical with the traditional license in late 1998.

In May 1999, stewardship of the X Window System passed from the Open Group to X.Org, a non-profit organization focused exclusively on maintenance and further development of the X Window System. X.Org supervised the release of X11R6.5.1.


Aficionados commonly refer to the X Window System as "X11" or simply as "X", but frown on the widespread but incorrect label "X Windows", analogous to "Microsoft Windows." A T-shirt seen at an X11 conference bore the sentiment: "It's a windowing system named 'X', not a system named 'X Windows.'"

See also

External link


From Wikipedia, the free encyclopedia. 
Modified by Geona