What causes page faults?

Question

According to Wikipedia:

A page fault is a trap to the software raised by the hardware when a program accesses a page that is mapped in the virtual add

Answer 1

Operating Systems use paging to group items witch should be placed in physical memory and move them between physical memory and shared memory. most of the time, data items witch place in a single page, are related to each other. when data items in a page are not used for a long time, operating system moves it to virtual memory to free some space in physical memory. and then when a page is required witch is in virtual memory, operating system moves it from virtual memory (hard disk) to physical memory. this is Page Fault !

and remember, different operating systems are different in paging algorithms.

Basics of Page Faults