UGC-NET Computer Science Operating Systems Questions with Explanation

In this Blog we are providing all the UGC-NET Computer Science previous year Questions with explanation:

Q : 1 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.

((UGC-NET Computer Science December 2014 Paper 2))

Answer: (B)

Explanation:

Time to serve  page fault if frame is empty or page replaced is not modified = 8 m.sec

Time to serve  page fault if page is modified = 20 m.sec

Frequency of Page modification  = 70% = 70/100 = 0.7

Frequency when page is not modified or frame is empty = (100-70)% = 30% = 30/100 = 0.3

Average access time = (0.3 * 8) + (0.7 * 20) = 2.4 + 14 = 16.4 m.sec

Hence correct option is (B) 16.4 m.sec.

This question was taken from UGC-NET Computer Science December 2014 Paper 2.