Unused physical memory frames are used by the OS for data caching
Page cache:
- Stores files in page sized chunks after being first accessed.
- OS looks ahead to find pages to load prior to usage.
- Allows quicker access times after being previously accessed
Buffer cache:
- Used to optimize access block devices
- Interposes read and write accesses as they are costly to slow device blocks and increase latency.
Swap cache:
- Tracks physical frames that have written out to swap files.
- When page has been swapped out it will remain in swap file slot when swapped back in.
- Swap file records file’s location in swap, to be input in page entry table.
- If a page is modified, then swap is expunged and rewritten as it has become dirty.
- This functionality reduces unnecessary swap file writebacks.