Updating segmentation schemes
Preventing this queue from being empty minimizes the computing necessary to service a page fault.
Some operating systems periodically look for pages that have not been recently referenced and perform page stealing, freeing the page frame and adding it to the free page queue.
When pure demand paging is used, pages are loaded only when they are referenced.
For simplicity, main memory is called "RAM" (an acronym of "random-access memory") and secondary storage is called "disk" (a shorthand for "hard disk drive"), but the concepts do not depend on whether these terms apply literally to a specific computer system. A swapped-out program would be current but its execution would be suspended while its RAM was in use by another program.
A program might include multiple overlays that occupy the same memory at different times.
The pages most frequently accessed are called the working set.
When the working set is a small percentage of the system's total number of pages, virtual memory systems work most efficiently and an insignificant amount of computing is spent resolving page faults.