Guided path: Memory deep dive
Step 3 of 6
Paging & page faults
How Windows brings pages in from disk and when the page file is used.
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Why it matters
Stutters, swap storms, and 'out of memory' behavior are often paging decisions, not just total RAM size.
Mental model
A valid virtual address does not mean the page is in RAM right now. A page fault is Windows fetching or creating the backing page.
Go one level deeper
Extra detail for readers who want more precision before opening a child topic.
- Transition PTEs describe pages being read from disk or zeroed on first touch.
- Hard faults show up in Performance Monitor as 'Pages/sec' with disk correlation.
How it works
- 1A reference to a non-resident valid page triggers a page fault.
- 2The Memory Manager locates the backing store (file mapping, heap, image, or page file).
- 3Modified pages may be written to the page file before their physical frame is reused.
Key terms
- Page fault
- A trap taken when a referenced page is not resident.
- Page file
- Disk space used to hold evicted private pages.
- Soft fault
- Fault resolved without disk I/O (e.g. demand-zero or already in memory elsewhere).
First touch after allocation
Many allocations commit virtual address space first; the first write can fault in a zeroed physical page on demand.
Common misconception
High page fault rate does not always mean disk thrashing. Many faults are cheap soft faults.
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