Question

Explain the following term with respect to virtual memory:

Demand paging

Answer 1

• In demand paging, a page is loaded into main memory only when it is requested.
• When a process is created, it initially has no pages in main memory. As the process starts execution, the program counter points to the first instruction, whose address lies outside main memory. This results in a page fault, causing the operating system to load the required page into memory.
• As page faults continue to occur, the operating system keeps loading the newly referenced pages. This method of loading pages is known as demand paging.
• A disadvantage of demand paging is that some pages which were used earlier but are no longer needed may still remain in memory unnecessarily.