GATE CS 2019 Set 1 — Question 11
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Computer Organization & Architecture → Memory Hierarchy & Cache → Cache Numericals
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Question
A certain processor uses a fully associative cache of size 16 kB. The cache block size is 16 bytes. Assume that the main memory is byte addressable and uses a 32-bit address. How many bits are required for the Tag and the Index fields respectively in the addresses generated by the processor?
Correct answer
(D) 28 bits and 0 bits
Solution
Given:
Since any block from main memory can be placed in any line of the cache, there is no need for a set index. Thus, the Index field is 0 bits.Block Offset:
Determined by the block size.
bits.Tag:
The remaining bits of the address are used for the Tag.
bits.So, Tag = 28 bits, Index = 0 bits.
- Cache Size = 16 kB = bytes
- Block Size = 16 bytes = bytes
- Main Memory Address = 32 bits
- Mapping: Fully Associative
Since any block from main memory can be placed in any line of the cache, there is no need for a set index. Thus, the Index field is 0 bits.Block Offset:
Determined by the block size.
bits.Tag:
The remaining bits of the address are used for the Tag.
bits.So, Tag = 28 bits, Index = 0 bits.
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