Editing Page fault (section)

{{Short description|Error from a process accessing unmapped memory}}
{{More footnotes|date=February 2008}}

In computing, a '''page fault''' is an [[Exception handling|exception]] that the [[memory management unit]] (MMU) raises when a [[Process (computing)|process]] accesses a [[memory page]] without proper preparations. Accessing the page requires a mapping to be added to the process's [[virtual address space]]. Furthermore, the actual page contents may need to be loaded from a back-up, e.g. a [[disk storage|disk]]. The MMU detects the page fault, but the operating system's [[Kernel (operating system)|kernel]] handles the exception by making the required page accessible in the physical memory or denying an illegal memory access.

Valid page faults are common and necessary to increase the amount of memory available to programs in any operating system that uses [[virtual memory]], such as [[Windows]], [[macOS]], and the [[Linux kernel]].<ref>{{cite book |last1=Bovet |first1=Daniel |last2=Cesati |first2=Marco |title=Understanding the Linux Kernel |date=November 2005 |publisher=O'Reilly Media |isbn=0-596-00565-2 |edition=3rd |url=http://gauss.ececs.uc.edu/Courses/c4029/code/memory/understanding.pdf |access-date=9 October 2021}}</ref>