Direct-mapped cache

In direct-mapped cache, each block in memory maps to a **single**, **specific** cache block.

For a direct mapped cache consisting of $N$ blocks: ?

• Block $X$ of main memory maps to cache block $Y$.
• $Y=X\mathrm{mod}N$

To find out which block actually resides in a cache block at any given time we use a tag field which distinguishes one memory block from another.

A direct-mapped cache address is composed of the following: ?

• The $\text{block field}$: number of bits required to address all cache blocks.
• The $\text{offset field (word field)}$: the number of bits required to address all words within a block.
• The $\text{tag field}$: the number of bits left over after the block and offset. Formatted as such: $001101110$ ($\text{tag}$, $\text{block}$, $\text{word}$).

title: Remember the order: $\color{blue}\textsf{tag}$, $\color{red}\textsf{block}$, $\color{green}\textsf{word}$