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GATE CSE 2023 Q64: TAG bits of a 64 KB 8-way set-associative cache

Question

An 8-way set associative cache of size 64 KB (1 KB = 1024 bytes) is used in a system with 32-bit address. The address is sub-divided into TAG, INDEX, and BLOCK OFFSET.

The number of bits in the TAG is _______.

Try it: numerical answer: type the value

Numerical answer. No negative marking.
Show answer and explanation

Answer: 19 (official GATE 2023 final answer key)

Concept used: INDEX + OFFSET bits together address one way of the cache, i.e. cache size / associativity.

First step: Note that INDEX + OFFSET =log⁡2(64 KB/8)=13= \log_2(64\text{ KB}/8) = 13 bits, whatever the block size.

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Source: official GATE 2023 CS question paper and final answer key, organised by IIT Kanpur. Question paper · Answer key

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