= Solution
<FIFO page replacement> orders resident pages by when they were loaded and evicts the oldest arrival. An access to a resident page does not change this order, so an old but heavily used page can be the next victim.
<LRU replacement> records the recency of every page access and evicts the page whose most recent access is oldest. It makes use of <temporal locality>, but exact reference tracking can require expensive per-access hardware or software bookkeeping.
<CLOCK page replacement> arranges frames in a circle with a scanning hand and one reference flag per frame. A use sets the flag. During replacement, the hand clears a set flag and moves on, giving that page another chance; it selects an eligible frame with a clear flag. Recent pages tend to survive a scan. <CLOCK page replacement> approximates recency rather than preserving the exact <LRU replacement> ordering. A dirty victim must be written back before its frame is reused, and pinned frames must be skipped.
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