catflap.org Online Dictionary Query

  context switch
       
           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)