Operating Systems - Page Replacement - FIFO, LRU, Optimal Algorithm
Trace the sequence of page faults when using the FIFO algorithm with 3 frames for the reference string: 1, 2, 3, 4, 1, 2, 5, 1, 2, 3, 4, 5. How many page faults occur?
Trace the sequence of page faults when using the FIFO algorithm with 3 frames for the reference string: 1, 2, 3, 4, 1, 2, 5, 1, 2, 3, 4, 5. How many page faults occur?
easy🧠🧾 Concept Trace Q12 of Q15
Step-by-Step Solution
Step 1: Initialize FIFO with empty frames
Frames: []Step 2: Process each page in order
1 -> fault, frames: [1]
2 -> fault, frames: [1,2]
3 -> fault, frames: [1,2,3]
4 -> fault, evict 1, frames: [4,2,3]
1 -> fault, evict 2, frames: [4,1,3]
2 -> fault, evict 3, frames: [4,1,2]
5 -> fault, evict 4, frames: [5,1,2]
1 -> hit
2 -> hit
3 -> fault, evict 1, frames: [5,3,2]
4 -> fault, evict 2, frames: [5,3,4]
5 -> hitStep 3: Count faults
Total faults = 9Final Answer:
Option B -> Option BQuick Check:
FIFO evicts oldest page regardless of future use, causing 9 faults here.
Quick Trick: FIFO faults count equals number of unique pages plus evictions [OK]
Common Mistakes:
MISTAKES- Counting hits as faults
- Misordering evictions in FIFO
- Forgetting to update frames after eviction
Trap Explanation:
PITFALL- Options with 7 or 8 faults underestimate evictions; 10 faults overcount by treating hits as faults.
Interviewer Note:
CONTEXT- Tests candidate's ability to mentally simulate FIFO page replacement and count faults accurately.
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