This section provides a quick introduction of the X Window System that offers a graphical user interface framework for any user applications.
What Is X Window System?
X Window System is a free windowing system that offers a framework for applications
to build graphical user interfaces (GUIs).
The X Window System was originally developed by a team of MIT developers led by Bob Scheifler and Jim Gettys.
Some features of the X Window System:
X Window System uses a client-server model: an X server the controls the graphical input and output,
and an X client sends data to the X server to display and receives user input from the X server for processing.
X Window System uses X network protocol for communications between a X server and a X client between remote machines.
This allows an application to run on one machine and interact with a user on another machine through X Window System.
X Window System provides no specification on user interface allowing multiple window managers to be developed
as user applications.
X Window System protocol has been revised several times. The most recent release is X11 published in 1987.
The picture below shows an early-1990s style Unix desktop running the X Window System