Compare FIFO, LRU, and Optimal page replacement algorithms.

When page fault occurs and memory is full, page replacement chooses which page to evict. FIFO removes oldest page - simple but suffers Belady's anomaly (more frames can cause more faults). LRU removes least recently used page - good approximation of optimal, implemented with timestamps or stack. Optimal removes page needed furthest in future - theoretically best but requires future knowledge, used as benchmark. LRU is practical compromise.