LRU Approximation Page Replacement Algorithm

Q1. Explain LRU Approximation Page Replacement Algorithm.

Ans. Few computer systems provide sufficient hardware support for true LRU page replacement. Many systems provide some help, however, in the form of a reference bit. The reference bit for a page is set by the hardware whenever that page is referenced (either a read or a write to any byte in the page). Reference bits are associated with each entry in the page table.

Initially, all bits are cleared (to 0) by the operating system. S a user process executes, the bit associated with each page referenced is set (to 1) by the hardware. After some time, we can determine which pages have been used and which have not been used by examining the reference bits, although we do not know the orders of use. This information is the basis for many page replacement algorithms that approximate LRU replacement.

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