Explain page replacement algorithm & find out page fault for following string using LRU method.6,0,12,0,30,4,2,30,32,1,20,15(Consider page frame size=3)

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written 2.7 years ago by

binitamayekar ★ 6.6k

LRU Page Replacement Policy

LRU stands for Least Recently Used page replacement strategy.
This algorithm works on the principle of “Last in First out“.
It replaces the newest page that arrived at last in the main memory.
It replaces the page that has not been referred by the CPU for the longest time.
It is implemented by keeping track of all the pages in a stack.
This strategy helps OS to find page usage over a short period of time.
This policy should be implemented by associating a counter with an even page.
Page, which has not been used for the longest time in the main memory, is the one that will be selected for replacement.
Easy to implement, keep a list, replace pages by looking back into time.

Example:

String = 6, 0, 12, 0, 30, 4, 2, 30, 32, 1, 20,15

Frame Size = 3

String	6	0	12	0	30	4	2	30	32	1	20	15
Frame 3			12		12	4	4		32	32	32	15
Frame 2		0	0		0	0	2		2	1	1	1
Frame 1	6	6	6		30	30	30		30	30	20	20
Miss/Hit	M	M	M	H	M	M	M	H	M	M	M	M

Page Fault = 10

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