Multi-tasking

Multitasking operating systems are a subset of operating systems - now, by far the predominant form - which allow multiple programs to run at the same time. There are two principal types: preemptive multitasking, in which computations can be (unkownst to them) interrupted in the middle of their work to allow other computations to run, and cooperative multitasking, in which a running computation has to explicitly 'give up' the machine, in order for another computation to run.