Operating-Systems

Question 20

Recall that Belady’s anomaly is that the page-fault rate may increase as the number of allocated frames increases. Now, consider the following statements:
S1: Random page replacement algorithm (where a page chosen at random is replaced) suffers from Belady’s anomaly
S2: LRU page replacement algorithm suffers from Belady’s anomaly
Which of the following is CORRECT?

A	S1 is true, S2 is true
B	S1 is true, S2 is false
C	S1 is false, S2 is true
D	S1 is false, S2 is false

Operating-SystemsPage-Replacement-AlgorithmGATE 2017 [Set-1]Video-Explanation

Question 20 Explanation:

FIFO may suffer from Belady’s anomaly not always FIFO suffer from Belady’s anomaly.
Page replacement algorithm suffers from Belady’s anomaly when it is not a stack algorithm.
S1: Random page replacement algorithm is not a stack algorithm. So, S1 is true.
S2: LRU is a stack algorithm. Therefore, it doesn’t suffer from Belady’s anomaly. S2 is false.

Correct Answer: B

Question 20 Explanation:

FIFO may suffer from Belady’s anomaly not always FIFO suffer from Belady’s anomaly.
Page replacement algorithm suffers from Belady’s anomaly when it is not a stack algorithm.
S1: Random page replacement algorithm is not a stack algorithm. So, S1 is true.
S2: LRU is a stack algorithm. Therefore, it doesn’t suffer from Belady’s anomaly. S2 is false.

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