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GO Classes CS Test Series | Operating Systems | Subject Wise Test 3 | Question: 23

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Consider in a system the following page replacement policies are used:

  • FIFO (First-In First-Out): Evicts the page that entered memory earliest.
  • LRU (Least Recently Used): Evicts the page that was least recently referenced.
  • OPT (Optimal): Evicts the page that will not be used for the longest time in the future.

Which of the following statements is/are correct?

  1. LRU can never perform worse than FIFO for the same reference string and number of page frames.
  2. LRU and FIFO perform the same when all referenced pages are distinct.
  3. FIFO suffers from Belady's anomaly, but LRU and OPT do not.
  4. Increasing the number of frames in FIFO incurs the same page misses as of LRU.

1 Answer

1 1 vote
A: False; LRU Can have more misses then FIFO
Consider the reference string and number of page frames 3

$123412512345$

FIFO: 9 miss

LRU: 10 miss

B: True; LRU works the same as FIFO when referenced pages are distinct. Consider the reference string and number of page frames 3

$12345678123$

D: False; increasing the number of page frames in FIFO does not improve the rate page misses then LRU, maybe it becomes worse than itself due to Belady's anomaly.
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