Assume a main memory with four page frames (frame A through frame D). Assume tha

Question

Assume a main memory with four page frames (frame A through frame D). Assume that the sequence of pages requested by a process is as shown below. 1, 6, 3, 2, 1, 5, 3, 7, 1, 4, 5 For each reference in the above sequence, identify whether it will cause a page fault (F) or will result in a page hit (H), when using the second chance page replacement algorithm. Use the table provided for your solutions - use the Status column to indicate F or H and the Page Frame column to indicate the page frame into which the page has been loaded. Assume that all page frames are initially empty.

Explanation / Answer

SOLUTION :-

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Explanation :-

The given page refrence sequence is

1,6,3,2,1,5,3,7,1,4,5

A) Given that all the frames are empty. so the first four refrences are page faults and pages 1,6,3,2 are  swap in the Frames A,B,C,D respectively. and refrence bit set to 1.

B) Next refrence to page 1 which is in frame A so it is a Hit. No change in refrence bit.

C) Next refrence is page 5 which is not exist so it is a fault. Now the OS replace the Page with refrence bit 1 which is Last recently used so page 1 will be replaced and page 5 swapped in. Refrence bit set to 1 and all other refrence bits are cleared 0 because after this replacement all refrence bits will be 1.

D) Next refrence to page 3 which is in frame C so it is a Hit. No change in refrence bit.

E) Next refrence is page 7 which is not exist so it is a fault. Now the OS replace the Page with refrence bit 1 which is Last recently used so page 6 will be replaced and page 7 swapped in. Refrence bit set to 1.

F) Next refrence is page 1 which is not exist so it is a fault. Now the OS replace the Page with refrence bit 1 which is Last recently used so page 2 will be replaced and page 1 swapped in. Refrence bit set to 1.

G) Next refrence is page 4 which is not exist so it is a fault. Now the OS replace the Page with refrence bit 1 which is Last recently used so page 5 will be replaced and page 4 swapped in. Refrence bit set to 1 and all other refrence bits are cleared 0 because after this replacement all refrence bits will be 1.

H) Next refrence is page 5 which is not exist so it is a fault. Now the OS replace the Page with refrence bit 1 which is Last recently used so page 6 will be replaced and page 5 swapped in. Refrence bit set to 1.

So There are 9 Faults and two hits using a second chance replacement algorithm.

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Page Status PageFrame 1 F A 6 F B 3 F C 2 F D 1 H A 5 F A 3 H C 7 F B 1 F D 4 F A 5 F B

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