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Belady’s anomaly | Set-1

Consider Belady’s anomaly which causes more no. of page faults when number of frames are increased in some of the cases.
S1: Belady's anomaly may occur in a random page replacement policy where a random chosen page is replaced.
S2. Belay's anomaly will occur in LRU.
Which statement is true ?


Statement S1 is true as Random chosen page policy may not follow stack property.
Statement S2 is false because LRU will always follow stack property.

Ambikesh Kumar Singh @ambikeshkumarsingh
19 May 2019 01:48 pm

Belady Anamoly: Normally what happens when you increase the number of frame in main memory , number of page fault decreases,but some times in case of FIFO PAGE REPLACEMENT TECHNIQUE , this may not be true, ie on increasing no.of frames in main memory ,page fault may increase. The reason behind this is an alogoritham called as STACK ALOGORITHAM. According to STACK ALOGROTHAM: the memory references with n frames are subset of memory reference with more than n frames.But FIFO sometime does not follow "stack algoritham". That is the reason for Belady Anamoly.


So for statemets S1:  it may be true if random choosesn algoritham  is FIFO

S2: False, Belady Anamoly never happens in LRU, because LRU follow stack algorithm.