X11 Definition

X11 is the current version of the X Window System.

The X Window System, often referred to merely as X, is the dominant system for managing GUIs (graphical user interfaces) on Unix-like operating systems. It was initially conceived at the Massachusetts Institute of Technology (MIT) in 1984 as a way to provide easy access to computing resources for all students and make the existing assortment of incompatible workstations from different vendors work together. The initial version, designated version 1, was the first operating environment that was truly hardware- and vendor-independent.

X progressed rapidly, for example with version 6 being introduced in January 1985 and version 7, which supported color, being added a few months later. Version 9 was released in September of the same year, followed soon thereafter by version 10. By 1986, outside organizations were requesting X, and X10R3, which was released in February 1986, became the first version to achieve widespread deployment, with both Digital Equipment Corporation (DEC) and Hewlett-Packard introducing products based on it. X10R4, released in December 1986, was the final release of X10.

Although X10 was interesting and powerful, it had become apparent that a more hardware-neutral design would be desirable before X became too widely deployed. Such a large-scale redesign was beyond the resources available at MIT alone, but, fortunately, DEC, then one of the world's leading computer manufacturers, was willing to undertake the monumental project. The company began in May 1986 and, after months of beta testing, finally launched the first release of X11 on September 15, 1987. It was offered as free software under the same terms as X9 and X10.

DEC's X11 development effort was led by Robert Scheifler, who had received a degree in computer science at MIT, and the project was discussed extensively on mailing lists on the early Internet. X thus represents one of the first large scale open source software projects, and it set a precedent for the development of Linux, which began just a few years later.

The September release was replaced by X11R2 in January 1988. Among the subsequent releases were X11R3 in October 1988, X11R4 in December 1989 and X11R5 in 1991.

The milestone X11R6 (Version 11, Release 6) was launched in May 1994. It is still in use today, although it has been given a number of upgrades, including the addition of numerous new features. For example, X11R6.1, released in March 1996 featured the addition of X Double Buffer extension, X Keyboard extension and X Record extension, and the X11R6.3, introduced the following December, added Web functionality.

X11R6.8.0, released in September 2004, featured the addition of Distributed Multihead X, window translucency, XDamage, XFixes and XEvIE. This was followed nine days later by X11R6.8.1, which incorporated a security fix in libxpm.

The most recent revision as of August 2005 was X11R6.8.2, which was released on February 10, 2005. Major changes included bug fixes and driver updates.

Despite its great success, not everyone is happy with X11, or even with X in general. Major criticisms are that it is bloated and overly complex (e.g., it has roughly the same level of complexity as an operating system itself). However, nothing is likely to displace X11 for years to come because of its very widespread (and growing) use and the improvements that are continuing to be made to it.