Ramblings & ephemera

The X Window System defined

From Ellen Siever’s “What Is the X Window System” (O’Reilly Media: 25 August 2005):

X was intentionally designed to provide the low-level mechanism for managing the graphics display, but not to have any control over what is displayed. This means that X has never been locked into a single way of doing things; instead, it has the flexibility to be used in many different ways. Both the simplest window manager and the most complex desktop environment can, and do, use the X Window System to manage the display.

When you run the X Window System, the X server manages the display, based on requests from the window manager. The window manager is an application that is itself an X client, with responsibility for managing the appearance and placement of the windows on the screen.

X itself has no role in determining the appearance of the screen, or what users are allowed to do with windows. That is the job of the window manager. For example, some window managers allow you to double-click in a window’s title bar and roll up the window into the title bar like rolling up a window shade (this is referred to as shading). Other window managers don’t have that feature. X doesn’t care; it’s a window manager concern. The X server’s job is to provide the low-level support so the window manager and other applications can shade or not, as they choose.

The X server manages the display hardware. The server captures input events from the user via keyboard or mouse (or other input device) and passes the information to a client application that has requested it. It also receives requests from the application to perform some graphical action. For example, if you use your mouse to move a window on the screen, the X server passes the information to the window manager, which responds by telling the server where to reposition the window, and the X server performs the action. If the client is a calculator, such as xcalc, it might request that digits be displayed into the window as the user clicks on buttons to enter a number.

The window manager controls the general operation of the window system; in particular, it controls the geometry and aesthetics of your X display. With the window manager you can change the size and position of windows on the display, reshuffle windows in a window stack, and so on.

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