Working Set in Operating System:
Definition and Explanation:
A working set is a collection of pages, which is actively referenced by a
process. The working set of processes should be kept in main memory, to run
efficiently. Otherwise thrashing may occur repeatedly. A popular rule to avoid
thrashing is to give processes enough page frame to hold half of their virtual
A working set storage management policy is used to maintain the working sets of
active program in main memory. The decision to add a new process to the active
set of processes is decided on the basis of whether enough space is available in
the main memory to accommodate the working set of pages for the new process.
The working set of a process W (t,w) at time t is the set of pages referenced by
process during the process time interval t. process time means the time during
which a process has the CPU. The variable w is called the working set window
size. The working set storage management policy uses this size for effective
Working sets change during process execution. Pages are added or deleted and
critical changes may occur as the process requires a completely different
working set. The initial and subsequent working sets of a process may differ
completely in size and contents. It complicates the storage management under a
working set strategy.
The page referenced by the process during this time interval constitutes time
process's working set W (t, w).