Architecture
XFree86 consists of client libraries used to write X applications ("clients"), and an X server responsible for the display. Clients and servers communicate via the X protocol, which allows them to run on different computers.
The XFree86 server communicates with the host operating system's kernel to drive input and output devices, with the exception of graphics cards. These are generally managed directly by XFree86, so it includes its own drivers for all graphic cards a user might have. Some cards are supported by vendors themselves via binary-only drivers.
Since version 4.0, XFree86 has supported certain accelerated 3D graphics cards via the GLX and DRI extensions.
Because the server usually needs low level access to graphics hardware, on many configurations it needs to run as the superuser, or a user with UID 0. However, on some systems and configurations it is possible to run the server as a normal user.
It is also possible to use XFree86 in a framebuffer device, which in turn uses a kernel graphics card driver.
On a typical POSIX-system, the directory /etc/X11 includes the configuration files. The basic configuration file is /etc/X11/XF86Config (or XF86Config-4) that includes variables about the screen (monitor), keyboard and graphics card. The program xf86config is often used, although xf86cfg also comes with the XFree86 server and is certainly friendlier. Many Linux distributions used to include a configuration tool that was easier to use (such as Debian's debconf) or autodetected most (if not all) settings (Red Hat Linux and Fedora's Anaconda, SuSE's YaST and Mandrake Linux used to choose this path).
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