GATE CSE 2025 Session 2 Q47: Identify the page replacement policy from a frame trace
- Operating System
- 2 marks
- MSQ
- No negative marking
Question
Consider a demand paging system with three frames, and the following page reference string: 1 2 3 4 5 4 1 6 4 5 1 3 2. The contents of the frames are as follows initially and after each reference (from left to right):
| initially | 1* | 2* | 3* | 4* | 5* | 4 | 1 | 6* | 4 | 5 | 1* | 3* | 2* | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Frame 1 | - | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 6 | 6 | 6 | 6 | 6 | 2 |
| Frame 2 | - | - | 2 | 2 | 4 | 4 | 4 | 4 | 4 | 4 | 4 | 1 | 1 | 1 |
| Frame 3 | - | - | - | 3 | 3 | 5 | 5 | 5 | 5 | 5 | 5 | 5 | 3 | 3 |
The *-marked references cause page replacements.
Which one or more of the following could be the page replacement policy/policies in use?
Try it: multiple select: one or more correct options
Show answer and explanation
Answer: D (official GATE 2025 final answer key)
Concept used: Check each policy at every replacement: which victim would it choose?
First step: At the reference to 4, frames hold 1, 2, 3 and page 2 is evicted; LRU would evict 1, while page 2 is the one used farthest in the future.
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Source: official GATE 2025 Session 2 CS question paper and final answer key, organised by IIT Roorkee. Question paper · Answer key
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