GATE CSE 2022 Q64: Page fault rate with LRU and four frames

Consider a demand paging system with four page frames (initially empty) and LRU page replacement policy. For the following page reference string

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

the page fault rate, defined as the ratio of number of page faults to the number of memory accesses (rounded off to one decimal place) is_________.

Try it: numerical answer: type the value

Your answer

Numerical answer. No negative marking.

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Answer: 0.6 (official GATE 2022 final answer key)

Concept used: LRU evicts the page whose last use is furthest in the past.

First step: Simulate the 15 references with 4 frames, marking faults; the first four distinct pages (7, 2, 3, 5) all fault.

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Source: official GATE 2022 CS question paper and final answer key, organised by IIT Kharagpur. Question paper · Answer key