Q. In a demand paging memory system, page table is held in registers. The time taken to service a page fault is 8 m.sec. if an empty frame is available or if the replaced page is not modified, and it takes 20 m.secs., if the replaced page is modified. What is the average access time to service a page fault assuming that the page to be replaced is modified 70% of the time ?
(A) 11.6 m.sec.
(B) 16.4 m.sec.
(C) 28 m.sec.
(D) 14 m.sec
Explanation: Let number of page faults be 100. In which 30 page faults are without modification so time is 30×8=240 m.sec. And rest 70 page faults are with modification so time is 20×70=1400 m.sec.
Average access time of servicing a page fault is (240+1400)/100=28 m.sec.