Schedulers
The selection process is carried out by the appropriate scheduler
Long-term scheduler (or job scheduler) – selects which processes should be brought into the ready queue
invoked very infrequently (seconds, minutes) (may be slow)
Control degree of multiprogramming
Number of processes in memory
Short-term scheduler (or CPU scheduler) – selects which process should be executed next and allocates CPU
invoked very frequently (milliseconds) (must be fast)