Page faults don’t always mean disk access
· One min read
A very common misconception in Operating Systems is that every page fault means the OS must access the disk.
That is not always true.
A page fault simply means that the required page is not usable in the current context.
This can happen for multiple reasons.
In many cases, the page is already present in main memory, but:
- the access permission is missing, or
- the page table entry is marked invalid temporarily.
In such situations, the operating system:
- Updates the page table entry
- Fixes the permission or state
- Resumes execution
➡️ No disk access happens here.
Disk access occurs only during a major page fault, when the page is truly absent from memory.
Understanding this distinction is important for:
- Performance analysis
- OS internals
- Interview questions related to virtual memory
This detail often separates a surface-level answer from a strong conceptual one.