XLIB Programming Manual, Rel. 5, Third Edition

1.2 X Window System Concepts

The X Window System is complex, but it is based on a few premises that can be quickly understood. This section describes these major concepts.

1.2.1 Displays and Screens

The first and most obvious thing to note about X is that it is a windowing system for bitmapped graphics displays.^[1] It supports color as well as monochrome and gray-scale displays.

A slightly unusual feature is that a display is defined as a workstation consisting of a keyboard, a pointing device such as a mouse, and one or more screens.^[2] Multiple screens can work together, with mouse movement allowed to cross physical screen boundaries. As long as multiple screens are controlled by a single user with a single keyboard and pointing device, they comprise only a single display, as shown in Figure 1-1.

Figure 1-1. A display consisting of more than one screen

1.2.2 The Server-Client Model

The next thing to note is that X is a network-oriented windowing system. An application need not be running on the same system that actually supports the display. While many applications can execute locally on a workstation, other applications can execute on other machines, sending requests across the network to a particular display and receiving keyboard and pointer events from the system controlling the display.

At this point, only TCP/IP and DECnet networks are supported by the X Consortium and most vendors, ...