Question

6. a) Consider a direct mapped cache with 10 blocks of 10 words each. Suppose main memory is 1000 words. For each memory address below say what cache block it maps to, what is the offset, and what is the tag. 934, 666, 348, 522

Answer 1

A direct mapped cache is the simplest and modest approach, where each main memory address maps to exactly  one cache block. For instance, on the right is a 16 byte main memory with a 4 byte cache ( for 1-byte blocks ).

Cache block - It is the basic unit of cache storage. It may have multiple bytes / words of data. There are 16 Bytes in Cache block.

Offset corresponds to the bits used to define the byte that to be accessed from the cache line.

Tag - It is a unique identifier for a group of data. Because a memory can be mapped in different regions of block, a Tag is used to differentiate between them.

Considering the given problem, where it supposes the main memory is 1000 words. And a word is defined to be a 32 - bits. So, here 'Word addressable' cache block is used, where smallest accessible chunk is 32 bits.

if the main memory is 1000 words. and each word is a 32 bits. i.e. 1000 * 32 = 32000 bits.

Block offset is equal to memory address / 2 to the power of n.

if there are 32 bytes which is equal to 2 to the power of 5, Therefore Offset is 5 Bits.

And, Tag is all the bits that are left in address space.