Virtual Memory and Page Replacement Questions and Answers

Q: Consider a program that consists of 8 pages (from 0 to 7) and we have 4 page frames in the physical memory for the pages. The page reference string is : 1 2 3 2 5 6 3 4 6 3 7 3 1 5 3 6 3 4 2 4 3 4 5 1 The number of page faults in LRU and optimal page replacement algorithms are respectively (without including initial page faults to fill available page frames with pages) :

LRU gives 10 page faults and optimal gives 7.With 4 frames, the first four distinct pages (1, 2, 3, 5) fill the frames without being counted. Working through the string 1 2 3 2 5 6 3 4 6 3 7 3 1 5 3 6 3 4 2 4 3 4 5 1, LRU faults on 6, 4, 7, 1, 5, 6, 4, 2, 5 and 1, which is 10 faults. Optimal replacement always evicts the page used farthest in the future and faults seven times.The pairs 9 and 6, 9 and 7, and 10 and 6 each get one of the two counts wrong.

21.

Working set model is used in memory management to implement the concept of

A.Swapping
B.Principal of Locality
C.Segmentation
D.Thrashing

Exam Year(s)

UGC NET - 2013,

Answer: B

The working set model is used in memory management to implement the principle of locality. A process refers during a short time only to a small set of pages, and the working set is the set of the pages it has used in its most recent references, which the system tries to keep in memory. The answer is (B).

Swapping and segmentation are other memory techniques, and thrashing is the trouble that arises when the working sets do not fit in memory, which the model is meant to prevent, so it is not what the model implements.

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22.

Consider a main memory with 3 page frames for the following page reference string : 5, 4, 3, 2, 1, 4, 3, 5, 4, 3, 4, 1, 4 Assuming that the execution of process is initiated after loading page 5 in memory, the number of page faults in FIFO and second chance replacement respectively are

A.8 and 9
B.10 and 11
C.7 and 9
D.9 and 8

Exam Year(s)

UGC NET - 2013,

Answer: D

The numbers of page faults are 9 for FIFO and 8 for second chance, which is the option '9 and 8'. The count does not include the first load of page 5, as the question says execution begins after it is loaded.

Under FIFO, the loads that fault are 4, 3, 2, 1, 4, 3, 5, 1 and 4 in the later steps, and together they give 9 faults after the first page. With second chance, a page that was referred to is spared once, which saves one fault, giving 8. The pairs 8 and 9, 10 and 11, and 7 and 9 do not match these counts.

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23.

Consider a program that consists of 8 pages (from 0 to 7) and we have 4 page frames in the physical memory for the pages. The page reference string is : 1 2 3 2 5 6 3 4 6 3 7 3 1 5 3 6 3 4 2 4 3 4 5 1 The number of page faults in LRU and optimal page replacement algorithms are respectively (without including initial page faults to fill available page frames with pages) :

A.9 and 6
B.10 and 7
C.9 and 7
D.10 and 6

Exam Year(s)

UGC NET - 2014,

Answer: B

LRU gives 10 page faults and optimal gives 7.

With 4 frames, the first four distinct pages (1, 2, 3, 5) fill the frames without being counted. Working through the string 1 2 3 2 5 6 3 4 6 3 7 3 1 5 3 6 3 4 2 4 3 4 5 1, LRU faults on 6, 4, 7, 1, 5, 6, 4, 2, 5 and 1, which is 10 faults. Optimal replacement always evicts the page used farthest in the future and faults seven times.

The pairs 9 and 6, 9 and 7, and 10 and 6 each get one of the two counts wrong.

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Virtual Memory and Page Replacement Questions and Answers

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