X has been around for a long time, and is well understood. It is based upon the client/server model we have explored throughout this course. The clients are those applications we wish to run on our machines in order to "get the work done". Typical clients are Mozilla Firefox, Ximian's Evolution, an Xterminal such as RXVT, or an application like DaliClock. In short, clients are those programs we normally see on the X display.

The server on the other hand is, in the case of Linux, usually the Xfree86 server. The server is responsible for interacting with the hardware. It's job is to be able to render an image, line, font or graphic using the hardware at it's disposal. Perhaps that hardware may be a state-of-the-art video card and a flat-panel LCD display, or it may be an old video card and a CRT display.

What makes X so versatile is that is does not constrain the client and the server to be on the same machines. In the simplest case, in order to be able to play KAsteroids on your Linux machine, you will be required to run both the client (KAsteroids) and the server (Xfree86) on the same machine. However, this needn't be the case. You may very well run KAsteroids on machine A, but use machine B's server to affect the display. In fact, X is so versatile that it can be used with remote procedure calls (RPC's) to between the client and the server. We'll return to this in due course, but we first need to understand how the X server interacts with the client windows.

Lets's give an example. Every client must have the ability to close windows, move them around the screen, minimise/maximise the windows, bring a window to the foreground or push it to the back, Etc. How does the X server handle all these functions?

It doesn't. It has an assistant to perform these tasks on it's behalf. Enter the window manager. The window manager has the task of beautifying the windows, allowing them to be placed here and there on the screen, allowing the user to minimize or close a window, Etc. In fact, as far as X is concerned, the window manager is yet another client - a bit like KAsteroids. (Bet you can tell I like that game!).

Now, of course there are those individuals that like "this" way of doing things rather than "that" way - and have written a window manager according to their taste. And since tastes vary considerably, so do window managers. Some (like twm) are very simplistic and functional, while others like enlightenment are complex beasties with all the bells and whistles you would expect from the most complex Space Shuttle dashboard. And of course, many in between like fvwm, icewm, Etc.

Probably the most basic functionality one would require from a window manager (apart from putting a nice border around every window and some snazzy buttons in the corners to enlarge or shrink a window, close or minimize, maximize, Etc.) is a way to launch an application. After all, if we can't launch applications, then what is the use of all these nice buttons and borders. So, window managers usually provide a means of launching applications from menus, from a command prompt or other more complex methods. How each does it is not standardized either - primarily because the X server is not dictating the way the end product should work or look.