What is page in and page out?

Answer 1

Page in and page out are actions taken by a virtual memory manager (VMM) as it adjusts the assignments of the memory mapping hardware. When a reference is made to a non mapped page, a page fault occurs. The VMM finds a page to release, usually the least recently used page, and checks it. If it is dirty, i.e. modified since loaded, the VMM pages it out by writing a copy to the page file. Then the VMM adjusts the mapping registers and locates the referenced page, either in the page file or in the executable image, and pages it in by reading the copy into memory. The faulting instruction is then restarted. Please see the discussion page.