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Page Fault

An exception raised by the MMU when a program tries to access a page that is not currently mapped in physical memory.

Categoryhardware

Overview

A page fault is not necessarily an error. It is the mechanism the OS uses to implement demand paging. When a fault occurs, the CPU traps to the OS, which then loads the required page from disk into RAM and updates the page table.

Types

  • Soft Page Fault: The page is in RAM but not mapped in the process's page table (fast to fix).
  • Hard Page Fault: The page must be read from the disk (very slow).
  • Invalid Page Fault: The program tried to access memory it doesn't own (results in a 'Segmentation Fault' or 'Access Violation').