What is X / What is X Server / What is XFree86?

Separation of Graphical Interface and Operating System

One major difference that you will notice in Linux is the separation of the Graphical Interface from the underlying operating system. Other OSes, such as Microsoft Windows ©, do not allow the user to run a fully functional OS without a graphical interface running also. This may, at first, seem to be an unimportant feature; however, this gives the user much greater control when things do go awry.

How many times has your computer locked up and you had to reboot?
What about Unused Resources?

Due to the separation of the OS and the Graphical User Interface (GUI), many issues can be caught and corrected before your computing session has to come to a halt. Also, servers run with fewer used resources when a GUI is not making needless use of RAM and CPU.

Remote X Sessions

Another important aspect of an X Server is that remote computers (other computers on the network or over the Internet) are able to use the graphical desktop on the computer running X (if the person running the computer so chooses, but this setting is not enabled by default). This allows a client to run applications which they would otherwise not have the required resources or software.

X Applications Required

It is also critical to understand that X is responsible for creating a graphics system for your computer. To make any sort of use of X, you need graphical applications written for X. Applicatons can be word processing programs, games, etc, or they can also be entire Desktop Applicatons (such as the KDE and Gnome Window Managers / Graphical Desktops). Many applications for X are included in the major Linux Distributions

The most widely used version of X is XFree86, which ships standard and is used by default, with most Linux Distros.

For more information about the most popular X Server for Linux, XFree86, please visit the XFree86 project page at http://www.xfree86.org