from
The Free On-line Dictionary of Computing (8 July 2008)
pre-emptive multitasking
<operating system, parallel> A type of {multitasking} where
the {scheduler} can interrupt and suspend ("swap out") the
currently running task in order to start or continue running
("swap in") another task. The tasks under pre-emptive
multitasking can be written as though they were the only task
and the {scheduler} decides when to swap them. The scheduler
must ensure that when swapping tasks, sufficient state is
saved and restored that tasks do not interfere.
The length of time for which a process runs is known as its
"{time slice}" and may depend on the task's priority or its
use of resources such as memory and I/O.
{OS/2}, {Unix} and the {Amiga} use pre-emptive multitasking.
This contrasts with {cooperative multitasking} where each task
must include calls to allow it to be {deschedule}d
periodically.
(1995-03-20)