Access to an un-mapped virtual address causes a page fault:
- which is a hardware interrupt
- we may kill the process; ‘segmentation fault’
- the OS may handle the page fault and do something interesting:
- lazily allocate physical memory
- allocate and lazily load files into memory
- provide virtual memory via page swapping
- provide memory-mapped files; create the illusion that files on the disk are resident in the address space
- emulate the access