XFree86 Definition

XFree861 is one of the most widely used implementations of the X Window System.

The X Window System, often referred to merely as X, is a complete, cross-platform and free client-server system for managing graphical user interfaces (GUIs) on single computers and on networks of computers. It is one of the most powerful and useful software packages for Unix-like operating systems.

XFree86 includes an X server (inclusive of drivers for all common graphic cards), libraries for the X clients (i.e., applications) and documentation. It runs primarily on Unix-like operating systems, including Linux, all of the BSD systems, Solaris and Mac OS X, and can also run on the Microsoft Windows systems via Cygwin (a Unix-like environment for such systems), and it supports the Intel-compatible, Alpha, PowerPC and Sparc processors together with a wide range of video cards and monitors.

XFree86 is developed by the XFree86 Project, Inc., a nonprofit organization that distributes it and its source code at no cost to users. The project was begun in 1992 as an effort to correct defects in X11 version X386, which had been released around 1990. Its name is a pun based on the fact that newer versions of the original X386 (i.e., non-free X-three-eighty-six) were being sold commercially.

From the early 1990s through the early 2000s XFree86 was the source of most innovation in X, and XFree86, was it used almost universally by Linux and the BSDs. Unfortunately, some conflict occurred within the organization in 2003 which resulted in Keith Packard, a noted X developer, being removed from the core development team and that team voting to disband. This was followed by a controversial change2 in licensing, beginning with the release of XFree86 4.4 in February 2004, that added a clause that its critics claim is similar to the much despised advertising clause in the old version of BSD-style licenses3.

This change made XFree86 incompatible with the GNU General Public License (GPL), by far the most commonly used license for free software, at least in the opinion of much of the free software community4. Thus it resulted in XFree86 version 4.4 being excluded from many Linux distributions (i.e., versions) and from OpenBSD (one of the four main modern descendants of the original BSD) and a search for alternatives. OpenBSD and some other operating systems have forked (i.e., created new versions) of XFree86 from version 4.4 RC2, the last version released under the old license.

Other open source X servers include the Xserver project (led by Keith Packard) and the current X.Org reference implementation (the X.Org Foundation Open Source Public Implementation of X11, which is a fork of XFree86). is the original X foundation that has been maintaining the X11 code base from which XFree86 split off, and all of the non-XFree86 X projects are now generally working in cooperation with it.

As of January 2006 the most recent version of XFree86 was 4.5.0, which was released in March 2005. This version was also released under the controversial XFree86 1.1 license.

The official reason for the new license was "to ensure that the Project and its developers receive their full due for what they have given freely away these past 12 years."5 However, the argument could be made that the developers would receive more credit for their work if the licensing change had not been made so that their implementation could have continued to represent the X mainstream.

1The XFree86 Project's home page is

2This change was the insertion of the clause: 'The end-user documentation included with the redistribution, if any, must include the following acknowledgment: "This product includes software developed by The XFree86 Project, Inc ( and its contributors", in the same place and form as other third-party acknowledgments. Alternately, this acknowledgment may appear in the software itself, in the same form and location as other such third-party acknowledgments.'

3The BSD license is a class of extremely simple and very liberal licenses for computer software that was originally developed at the University of California at Berkeley (UCB). It was first used in 1980 for the Berkeley Source Distribution (BSD), also known as BSD UNIX, an enhanced version of the original UNIX operating system that was first written in 1969 by Ken Thompson at Bell Labs.

The so called advertising clause stated that all advertising materials that mention features of or use of the software must display the acknowledgment: "This product includes software developed by the University of California, Berkeley and its contributors." One of the problems with this clause arose from the fact that people who made changes to the source code often wanted to have their names added to the acknowledgment, which could easily result in large and cumbersome acknowledgments for products with numerous contributors and for software distributions consisting of multiple individual projects. A second problem was legal incompatibility with the terms of the GPL, because the GPL prohibits the addition of restrictions beyond those that it already imposes. In June 1999, after two years of discussion, the Office of Technology Licensing at UCB finally allowed the clause to be deleted.

4The XFree86 Project claims that there is no problem of compatibility with the GPL and that "Our Credit clause is Absolutely Not an advertising clause!"


Created January 16, 2006.
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