Basic X Concepts

The underlying engine of X11 is the X protocol, which provides a system of managing displays on local and remote desktops. The protocol uses a client/server model that allows an abstraction of the drawing of client windows and other decorations locally and over a network. An X server draws client windows, dialog boxes, and buttons that are specific to the local hardware and in response to client requests. The client, however, does not have to be specific to the local hardware. This means that system administrators can set up a network with a large server and clients and enable users to view and use those clients on workstations with totally different CPUs and graphics displays.

NOTE

As an example of X's support for remote client use, much of the original text of this chapter was written using the OpenOffice.org office suite, but the keyboard and display used for writing were part of a Sony VAIO laptop running Fedora; OpenOffice.org was launched from a Dell notebook running Fedora Core 3. Subsequent revisions were made on a workstation running Fedora Core 4, using the open-source OpenOffice.org office suite via a remote 802.11g connection from an IBM ThinkPad running Red Hat Enterprise Linux 4 WS.

X11's form of distributed processing means that Fedora, along with X11R6, can be used as a stable, cost-efficient desktop PC platform for using clients launched from a more powerful server, minicomputer, or mainframe. The X model provides a way to continue to use legacy PCs when more powerful systems are put in place, and it can help centralize the job of system management.

X is popular with Unix and Linux users, system administrators, and network engineers for a number of reasons. X is extremely portable and works with nearly every hardware-based graphics system on the market. This allows X to be deployed and used with high-end workstations and diminutive embedded devices. X also provides portable and multi-platform programming standards that truly allow write-once, cross-platform development.

Another attractive feature of X is its networking capabilities, which easily allow management of thousands of workstations, deployment of thin-client desktops, remote launching of applications, and standardization of installations all working over a variety of media, such as Ethernet and wireless network connections. Although early releases of X supported only a handful of display architectures, subsequent versions have enabled the use of compressed fonts, shaped (that is, non-rectangular) windows, and a graphical login manager, known as a display manager (see the section "Using a Display Manager," later in this chapter). X also provides a mechanism for customizing how X clients appear: It allows you to edit text files that contain window or button appearance settings. These settings, known as resources, are available for nearly every X11 client.

Many small office/home office (SOHO) environments and computer hobbyists run Linux and X locally on non-networked PCs. But small business, academic, corporate, and enterprise-class environments can also reap the benefits of adopting and using X and Fedora for network computing. By using X, administrative staff, users, and in-house developers can enjoy custom or standardized desktops, and applications can be stored in and launched from a single location. This can make the job of system and software maintenance a lot easier.