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Lesson 2 The X Windows System
Objective Function and basic installation of the X Windows System
What is the function and basic installation of the X Windows System?
The X Windows System is the foundation for Linux's graphical user interface (GUI). Often referred to as X, the X Windows System provides the necessary tools and functionality to make a GUI. These tools come from a collection of applications found in the various directories under /usr/X11R6/.
X Window System: A collection of programs which act as an intermediate layer between X applications and the computer video hardware, keyboard, and mouse.
GUI layers
GUI layers
Running X applications
Any application that conforms to the X standard can run as an X client, as long as an X server is running. The X server provides the interface between X applications, or "clients," and the video hardware. An additional benefit is that X clients do not need to run on the same machine as the X server. An X server and its clients can be across the world from each other.
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X client requests
To minimize overhead, the X server only performs basic display functions. X clients request services from the X server such as:
  1. Display a window
  2. Draw a blue box
  3. Send input to a program
  4. Rastera font
Raster: To apply all transformations (scaling, skewing, rotating, etc.) to a font and display a string of characters on a graphical display.
The server interprets these requests and responds by either granting or refusing the client's request for input or display. If the X server is unable to fill an X application's needs, it notifies the X application that the request is refused.

While it is possible to purchase and install a commercial version of X, Linux comes with XFree86 a freely available X server. XFree86 comes in source form, and it compiles on many different systems. Red Hat Linux provides packages containing the complete XFree86 source, documentation, libraries, binaries, and fonts.
XFree86: A popular implementation of the X11R6 X Window System standard used by many operating systems. XFree86 is the default X server for Red Hat Linux.
Installing XFree86
XFree86 installs as part of the default installation procedure. If, however, you elect not to install X Windows, XFree86 may be installed later via the rpm or gnoRPM .
Installing the XWindows System
The next lesson examines the factors that influence the installation of XFree86.