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GATE CSE 2021 Set 2 Q37: Write-through L1 read misses and write-allocate policy

Question

Assume a two-level inclusive cache hierarchy, L1 and L2, where L2 is the larger of the two. Consider the following statements.

S1S_1: Read misses in a write through L1 cache do not result in writebacks of dirty lines to the L2.

S2S_2: Write allocate policy must be used in conjunction with write through caches and no-write allocate policy is used with writeback caches.

Which of the following statements is correct?

Try it: multiple choice: exactly one correct option

Select one option
Wrong answer costs 2/3 mark in GATE.
Show answer and explanation

Answer: A (official GATE 2021 final answer key)

Concept used: A write-through cache never holds dirty lines; write allocate is usually paired with write-back, and no-write allocate with write-through.

First step: Ask whether a write-through L1 can ever have a line that differs from L2; then check which pairing of allocation policies is the usual one.

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Source: official GATE 2021 Set 2 CS question paper and final answer key, organised by IIT Bombay. Question paper · Answer key

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