A human-machine interface allows information to be exchanged between the human user and the machine. To make this communication the easiest to do and perform, we use different elements. Input devices, such as the keyboard, mouse, or scanner allow humans to give information or commands to the machine. Output devices such as the screen, LEDs or the printer allow the machine to respond to commands and display information. The screen will allow you to display simple text as well as a graphical environment. Thanks to this one will be able to display windows, images, animations (in 2 or 3 dimensions), and even videos.

• XFree86
  Free implementation of the X Window System graphics system. XFree86 works on most Unix-like operating systems and also on Windows using Cygwin.

• X.Org
  This is a fork of XFree86 created following a disagreement on the change of license of the latter.

• Xgl
  Free X server overlay of OpenGL via glitz, allowing to use the 3D capabilities of modern graphics cards in a traditional office environment, thus making possible display effects such as transparency, window rotations, shadows, etc. .