Question

onsider the following page reference string:

3, 8, 2, 9, 8, 2, 3, 9, 2, 8

1. Assuming demand paging with three frames, how many page faults would occur for the following replacement algorithms? Show your working. (10-marks)
   1. First in First out
   2. Least Recently Used
   3. Optimal Replacement
2. Calculate the no. of page faults for each algorithm. (3-marks)
3. Which algorithm performs best for the given reference string? (2-marks)

Answer 1

3,8,2,9,8,2,3,9,2,8

A. FIFO

Ref	3	8	2	9	8	2	3	9	2	8
F#1	3	3	3	9	9	9	9	9	9	9
F#2		8	8	8	8	8	3	3	3	3
F#3			2	2	2	2	2	2	2	8
H/F	F	F	F	F	H	H	F	H	H	F

Total number of page fault=6

B. RECENTLY USED

Ref#	3	8	2	9	8	2	3	9	2	8
F#1	3	8	2	9	8	2	3	9	2	8
F#2		3	8	2	9	8	2	3	9	2
F#3			3	8	2	9	8	2	3	9
H/F	F	F	F	F	H	H	F	F	H	F

TOTAL NUMBER OF PAGE FAULT=7

C. OPTIMAL PAGE REPLACEMENT

Ref#	3	8	2	9	8	2	3	9	2	8
F#1	3	3	3	9	9	9	9	9	9	8
F#2		8	8	8	8	8	3	3	3	3
F#3			2	2	2	2	2	2	2	2
H/F	F	F	F	F	H	H	F	H	H	F

TOTAL NUMBER OF PAGE FAULT = 6

Algorithm FIFO and Optimal page replacement both performs equally well in this case.

But usually OptimalPage Replacement gives better performance.

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