GNU/Linux is a multi-tasking OS; a part of the kernel called the scheduler keeps track of all the programs running and allots processor time accordingly, effectively running several programs simultaneously. Each process is allocated its own memory, and is forbidden by the kernel from accessing memory outside its alloted area. Different processes share data by means of common ``scratch pads'' in memory, rather than by writing directly onto each others' memory space. Consequently, if a program crashes, no other processes are affected. Unplanned rebooting with GNU/Linux is extremely rare.13 It is normal for a GNU/Linux system to run uninterruptedly for weeks or months without rebooting.
GNU/Linux is also a multi-user OS. This means not merely that several users can use a single machine, each having their own customized environments, but that several users may use a single machine at the same time, either by logging on from a terminal or another computer, or by leaving a running process after logging out. Out of the box, Mandrake supports six desktop sessions, which are accessed by pressing <ctrl>-<alt>-f1- f12; with enough terminals, six people can log onto your desktop machine and work in complete independence. The more users, the more memory is required and the slower the machine will respond, but if no one is running a program that hogs the processor they can all work at an acceptable speed.