ITPEC FE Morning April 2021 Question 18
Among the page replacement methods in virtual memory management, which of the following is the LRU control method?
Explanation
Replace the page not referenced for the longest time — LRU (least recently used) assumes a page that has been idle longest is least likely to be needed soon.
LRU records when each page in main memory was last referenced, hits included. On a page fault with no free frame, it evicts the page whose last reference is oldest.
Answer (d)
Why not others:
- •(a) — choosing by reference and change flags, preferring pages neither referenced nor changed, is NRU (not recently used)
- •(b) — picking a page at random with equal probability is random replacement
- •(c) — replacing the page that was loaded earliest is FIFO, which ignores how recently a page was used
Key rule: LRU goes by the time of the last reference, FIFO by the time of loading; a page that is used often but was loaded early is kept by LRU and evicted by FIFO.
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