<Table> <Tr> <Td> </Td> <Td> This article includes a list of references, but its sources remain unclear because it has insufficient inline citations . Please help to improve this article by introducing more precise citations . (February 2008) (Learn how and when to remove this template message) </Td> </Tr> </Table> <Tr> <Td> </Td> <Td> This article includes a list of references, but its sources remain unclear because it has insufficient inline citations . Please help to improve this article by introducing more precise citations . (February 2008) (Learn how and when to remove this template message) </Td> </Tr> <P> A page fault (sometimes called #PF, PF or hard fault) is a type of exception raised by computer hardware when a running program accesses a memory page that is not currently mapped by the memory management unit (MMU) into the virtual address space of a process . Logically, the page may be accessible to the process, but requires a mapping to be added to the process page tables, and may additionally require the actual page contents to be loaded from a backing store such as a disk . The processor's MMU detects the page fault, 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 . </P> <P> Contrary to what "fault" might suggest, valid page faults are not 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 macOS, Linux, * BSD, Solaris, AIX, and HP - UX), and z / OS . </P>

When do page fault occur in operating system