ITPEC FE Morning April 2018 Question 16

Accessing a mapped page that is not in physical memory — the hardware raises a page fault and the OS brings the page in.

In virtual memory the page table records which virtual pages are present in main memory. When a program touches a page that is valid in its address space but currently only on auxiliary storage, a page fault interrupt occurs; the OS reads the page in, replacing another page if memory is full, updates the page table and restarts the instruction. It is a normal event, not an error.

Answer (a)

Why not others:

• •(b) — a hardware error in memory is detected by error checking and raises a machine check interrupt; it is a failure, not a missing page
• •(c) — trying to hold more data than memory allows is an overflow or out-of-memory condition; virtual memory exists precisely so that programs larger than physical memory can run
• •(d) — several programs can legitimately share a page (such as shared library code); using a page another program also uses does not by itself cause a fault

Key rule: A page fault means "valid but not loaded" and is resolved by paging in; frequent page faults, not a single one, are the performance problem (thrashing).

Software · AI-written, may contain errors