Question

For the figure below, using the Clock policy of page replacements, show the figure after each of the following page requests:  
3, 2, 1, 5.

    -----
   | >5  |
   |  4* |
   |  2  |
    -----

Answer 1

Here 5 is the first page which was loaded into memory and page 4 has been referred more than once. Thus it would be given priority when a page has to be chosen for replacement.

Ref.	Initial	3	2	1	5
Frame#1	>5	3	3	1	1
Frame#2	4*	>4*	>4*	>4	5
Frame#3	2	2	2*	2*	>2
Hit/Fault	-	F	H	F	F

When page 3 was brought into frame, FIFO replacement technique was used. When page 2 was brought, ideally 4 should have been replaced, but since it has been referred more than once in past, it will be given one more chance and page 3 will be choosen as victim page.

Here total # of fault =3

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