Preemption refers to preempting or interrupting running computations to be resumed later, while cooperation means computations either run to completion or yield control back at suspension points.

A typical example of preemptive scheduling is operating system processes on a single-core processor; the processes allocate exclusive blocks of memory and can be executed independently, and the operating system periodically switches the active execution context between the processes to give an illusion of parallelism.

Preemption and cooperation are often used in the same systems at different layers of abstraction; for example, cooperative computations might also be periodically preempted to ensure a more fair distribution of processor time.