NIELIT 2016 MAR Scientist B - Section C: 38

Question

Determine the number of page faults when references to pages occur in the following order: $1,2,4,5,2,1,2,4$. Assume that the main memory can accommodate $3$ pages and the main memory already has the pages $1$ and $2$, with page $1$ having been brought earlier than page $2$.(LRU algorithm is used).

• A. $3$
• B. $5$
• C. $4$
• D. None of these.

Answer 1

Least Recently Used –
In this algorithm page will be replaced which is least recently used.

 

1

2

1).now  1 is already in memory so 1 hit

2.)now  2 is already in memory so 2 hit

3.)now  4 is not  in memory so  miss-FIRST page faults

1

2

4

4.)now  5 is not  in memory so miss according to LRU we replace with 1-SECOND page faults

5

2

4

5.)now  2 is already in memory so hit

6.)now  1 is not  in memory so  miss and we replace with 4 number page accordingly LRU-THIRD page faults

5

2

1

7.)now  2 is already in memory so 2 hit

8.)now  4 is not  in memory so miss according to LRU we replace with 5-FOURTH page faults

4

2

1

total number of page faults = 4

 

Answer 2

just put 1 and 2 is in memory before starting the LRU ALGORITHM….