Paging & Virtual Memory

Virtual Memory - giving the illusion of more physical memory than there really is (via demand paging) ƒ
 Pure Paging - The total program is kept in memory as sets of (non-contiguous) pages ƒ No illusion of virtual memory ƒ
 Demand Paging - A program’s “working set” is kept in memory, reference outside WS causes corresponding code to be retrieved from disk (“page fault”) ƒ Provides the illusion of virtual memory CS3204 - Arthur Paging Systems ƒ Processes (programs) are divided into fixed size pieces called Pages ƒ Main memory is divided into fixed size partitions called Blocks (Page Frames) ƒ Pure Paging - entire program is kept in memory during execution, but pages are not kept in contiguous blocks ƒ Demand paging - only parts of program kept in memory during execution, pages are not kept in contiguous blocks