ISRO CSE 2017 | Question: 52

Question

Given reference to the following pages by a program

0,9,0,1,8,1,8,7,8,7,1,2,8,2,7,8,2,3,8,3

How many page faults will occur if the program has three page frames available to it and uses an optimal replacement?

• A. 7
• B. 8
• C. 9
• D. None of the above

Answer 1

   0     9   0    1     8     1    8    7     8    7    1     2     8    2     7    8     2    3     8    3  

			1	1	1	1	1	1	1	1	2	2	2	2	2	2	2	2	2
	9	9	9	9	9	9	7	7	7	7	7	7	7	7	7	7	3	3	3
0	0	0	0	8	8	8	8	8	8	8	8	8	8	8	8	8	8	8	8

F    F    H    F    F    H     H    F   H     H    F    H   H    H    H    H    H    F    H    H

so total no. of page fault = 7

Comments

Draw hit also .

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for 3rd last ref. of 3, while choosing from current pg. 2,7,8 to remove, i applied opt. algo. but failed bcoz nxt there was not even 2 of them present in reg. to decide 3rd one to replace. so i totally applied fifo on all 3 and found 8 came first, so replaced with 8 but i should apply fifo in 2,7 only bcoz atleast 8 was safe by opt. algo. tried earlier.

Answer 2

Number of Page faults  = 7.

Hope it helps,

Comments

Which Replacement policy has been used please mention..

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 'and uses an optimal replacement'  - last few words of question itself