Page fault

A page fault (sometimes called #PF or PF) is a type of interrupt, called trap, raised by computer hardware when a running program accesses a memory page that is mapped into the virtual address space, but not actually loaded into main memory. The hardware that detects a page fault is the processor's memory management unit (MMU), while the exception handling software that handles page faults is generally a part of the operating system kernel. When handling a page fault, the operating system generally tries to make the required page accessible at the location in physical memory, or terminates the program in case of an illegal memory access.

Contrary to what the name "page fault" might suggest, page faults are not always errors and are common and necessary to increase the amount of memory available to programs in any operating system that utilizes virtual memory, including OpenVMS, Microsoft Windows, Unix-like systems (including Mac OS X, Linux, *BSD, Solaris, AIX, and HP-UX), and z/OS. Microsoft uses the term hard fault in more recent versions of the Resource Monitor (e.g., Windows Vista) to mean "page fault".