Demand paging (contd.)
There is only one physical address space but as many virtual address spaces as the number of processes in the system. At any time physical memory may contain pages from many process address space.
Pages are brought into the main memory when needed and “rolled out” depending on a page replacement policy.
Consider a 8K main (physical) memory and three virtual address spaces of 2K, 3K and 4K each. Page size of 1K. The status of the memory mapping at some time is as shown.