A page fault occurs when a process accesses a virtual memory page that is not currently mapped to a physical frame in RAM. The operating system’s memory manager handles the fault by locating the required page in secondary storage (such as a disk-backed swap area or file), then loads it into physical RAM, updating the page tables, and then resuming execution of the process.
Page faults are a normal and expected mechanism in virtual memory systems; however, a high rate of page faults can significantly degrade performance due to the latency of secondary storage access.
Example: An application attempts to access data that has been swapped out to disk, causing the operating system to load the corresponding page back into RAM and triggering a page fault.