Page Fault Definition Explained

A page fault occurs when a program attempts to access data or code residing in a specific page of virtual memory, but that page is not currently loaded into the physical memory (RAM).

Triggering a Page Fault

The fundamental reason for a page fault is accessing a required page that is absent from main memory. This triggers an exception handled by the Operating System (OS).

Steps in Page Fault Handling

• Program access attempt targets a page not in RAM.
• The Memory Management Unit (MMU) detects the missing page and generates an exception.
• The OS's page fault handler takes control.
• The OS finds the required page on secondary storage (disk).
• A free frame in RAM is allocated, or if necessary, an existing page is swapped out.
• The required page is loaded from disk into the allocated RAM frame.
• The process's page table is updated to map the virtual page to the physical frame.
• The instruction that caused the fault is re-executed successfully.

Why Option 2 is Correct

Option 2 correctly states that a page fault occurs "when a page currently not in a memory is accessed". This is the precise definition. The system needs the page, checks memory, finds it missing, and thus generates the fault.

Why Other Options Are Incorrect

• Option 1 describes normal memory access, not an error condition.
• Options 3 and 4 relate to page replacement, which is a *consequence* or *related process* managed by the OS during fault handling, not the direct cause of the fault itself. The fault happens because the page is *needed* and *missing*, irrespective of whether it might eventually be involved in a replacement operation.