Once an X server is running, X client applications can connect to it and create a GUI for the user. A range of GUIs are available with Red Hat Enterprise Linux, from the rudimentary Tab Window Manager (twm) to the highly developed and interactive desktop environment (such as GNOME or KDE) that most Red Hat Enterprise Linux users are familiar with.
To create the latter, more comprehensive GUI, two main classes of X client application must connect to the X server: a window manager and a desktop environment.
C.2.1. Maximum number of concurrent GUI sessions
Multiple GUI sessions for different users can be run at the same time on the same machine. The maximum number of concurrent GUI sessions is limited by the hardware, especially by the memory size, and by the workload demands of the running applications. For common PCs the maximum possible number of concurrent GUI sessions is not higher than 10 to 15, depending on previously described circumstances. Logging the same user into GNOME more than once on the same machine is not supported, because some applications could terminate unexpectedly.