Any computations and executions take place only when the program is
resided in the main memory and it is getting the CPU time. This state of
program is referred to as a process. Whenever a process undergoes computations
the necessary pages from the auxiliary storage are copied down in the physical
memory. At a particular instance of time the process may refer to the page that
is not yet resided in the physical
memory but still present in the auxiliary memory, such an unpredictable
condition is called a Page Fault. This condition is unpredictable, in
perspective with the operating system because the OS cannot determine what type
of page reference the process can make once the CPU is allocated to it.
Certain steps and procedure should be carried out by the OS whenever the
page fault is generated to make the page available to the process. First step
the OS follow is to determine if the page is valid in the auxiliary memory or
not. If not certain message are given to the process. But if it is valid then
certain calculations are carried out related to the page size and its content.
Then certain page in the physical memory is selected which must be replaced by
the requesting page, which is done by following certain page replacement
algorithms. Now the OS replaces the
requesting page with the existing page in the physical memory and finally
updates the page table and register values.
