Page Fault

The page table contains a field for the control bits – The control consists of valid bits, protection bits etc. – A valid bit is used in each page entry. • If the bit is on (1)  the page is in memory and the entry contains the physical addr. • If the bit is off (0)  the page is not present in main memory and a page fault occurs, • When a page fault occurs, the operating system must be given control. – This transfer is done with the exception mechanism • Once the OS gets control, – it must find the next page in the disk and – Decide where to place the requested page in main memory.