Virtual Memory

Question

A demand paging system takes 250 time units to service a page fault and 450 time units to replace a dirty page. Memory access time is 10 time units. The probability of page faults is 0.3. In case of a page fault, the probability of page being dirty is 0.06. The average access time is  ?

Comments

No answer is 85.6.

Can you please share your approach

Answer 1

average access time =page fault rate*(page fault service time )+page hit rate*(memory access time)

 here page fault service time= when page  is dirty + when page is not dirty

page fault  service time= (probability of  being page dirty*time taken to replace dirty page+ probability of not being dirty *service time)

average access time=0.3*(0.6*450+0.94*250)+0.7*10

average access time=85.6 unit time.

Comments

Can you please explain in more detail .

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Tell me what are you not getting??