context switch

operating system When a multitasking operating system

stops running one process and starts running another. Many

operating systems implement concurrency by maintaining

separate environments or "contexts" for each process. The

amount of separation between processes, and the amount of

information in a context, depends on the operating system but

generally the OS should prevent processes interfering with each

other, e.g. by modifying each other's memory.

A context switch can be as simple as changing the value of the

program counter and stack pointer or it might involve

resetting the MMU to make a different set of memory pages

available.

In order to present the user with an impression of parallism,

and to allow processes to respond quickly to external events,

many systems will context switch tens or hundreds of times per

second.

(1996-12-18)