Direct mapping - Computer System Architecture

Question 1 UGC NET June-2020
Consider a machine with a byte addressable main memory of 2¹⁶ bytes and block size of 8 bytes. Assume that a direct mapped cache consisting of 32 lines is used with this machine.
How many bits will be there in Tag, line and word field of format of main memory addresses?

A – 8,5,3

B – 8,6,2

C – 7,5,4

D – 7,6,3

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Answer- A
Explanation:
Direct mapped cache:
In a direct-mapped cache structure, the cache is organized into multiple set with a single cache line per set. Based on the address of the memory block, it can only occupy a single cache line. The cache can be framed as a (n*1) column matrix.

In above,
Main memory size = 2¹⁶B
Block size = 8 B = 2³ B , Block offset = 3
Cache line = 32 B = 2⁵ B, Cache line offset = 5

Tag bits = main memory offset – (line offset + Block offset)
= 16 – (5 + 3)
= 16 – 8 = 8