What is page fault?

In the computer storage technology a page fault is an exception which is raised by the memory management unit when a requested page isn't mapped in physical memory. This exception is passed on to the OS (operating system) which is able to then try to handle the exception by making the required page accessible at a location in physical memory.

For instance a page fault may take place when a program requests a page in memory and the system can't find it at the requested location. If the page is elsewhere in memory then the fault is called as a soft page fault. If the page should be retrieved from disk, the fault is called as a hard page fault.

Opposing to what its name might suggest a page fault is never a fatal error. Actually, it is a relatively normal occurrence in any OS operating system that utilizes virtual memory in order to increase the amount of memory available to programs. The term General Page Fault is habitually found printed on the screens of computers running a Microsoft Windows operating system when a serious error has take placed in the paging algorithms that handle an ordinary and generally harmless page fault. This kind of paging error takes place in the software handling the exception, and isn't directly related to the page fault itself, which take place in hardware.

Page faults by their extremely nature degrade a program's or operating system's performance and is able to cause thrashing.  Optimizing any or every program's memory usage and commonly making more physical memory available reduces the number of page faults that occur, and get better the program's or the entire system's performance.