Virtual Memory Faults

🟡 Q. What is the difference between a page fault and a segmentation fault?

Answer. A page fault is a CPU trap because a virtual page is not currently mapped as usable; it is often normal and recoverable. A segmentation fault is the process-visible failure after the OS determines that the access is invalid and cannot be satisfied.

On a valid page fault, the kernel may load a file-backed page, allocate a fresh zero page, or perform copy-on-write, update the page table, and restart the instruction. A major fault needs storage I/O; a minor fault can be resolved from memory.

If the address is outside mapped regions, violates permissions, or cannot be loaded, the kernel signals the process. The memorable distinction is: page fault is the mechanism; segmentation fault is one possible outcome.

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