I’ve seen the X-Windows system described as the “distributed, graphical method of working,” and that probably fits the best. It’s distributed because you could run the display on your monitor in Virginia even though the program is actually running on a computer in California or Calcutta, and it’s graphical because you see a lot of nice pictures on your screen.
Despite the extent to which it has spread in the UNIX world, the X-Windows system is not a UNIX product. The X-Windows system, affectionately called X, was developed by the Massachusetts Institute of Technology and runs on a wide range of computers, even MS-Windows-based versions.
The first version was developed at MIT in 1984. Several versions have been developed since, with the most current version, X version 11 (X11), first released in 1987. X11 has been adopted as the industry standard windowing system, with the support of a consortium of major computer industry companies such as DEC, HP, SUN, and IBM.
Although you could probably find a system that is still running release 5, the newest release (as of this writing) is release 6. You will see references to the release as X11Rn, where n is the release number. So, the current release would be X11R6.
In this section we are going to talk about the basics of the X-Windowing System,
rather than the desktop environments like KDE and Gnome. The reason is quite
simply that this material was first written in 1996 and neither KDE nor Gnome
had really established itself. A lot of things have happened in the meantime
and I just haven’t gotten around to updating this. Any volunteers?