Cache

A Cache is a system in which fast memory is used to accelerate access to a larger, but also slower main memory. The cache memory contains a copy of a portion of the content of the main memory.

Overview

Cache memory is fast memory that contains a copy of slower memory in the system. The purpose of the cache is to minimize delays experienced by the processor, thus making a system faster.

Caches are typically used in systems with clock speeds of 200 MHz and higher. In large systems, such as PCs and servers, there are typically multiple levels of caching, and these are labelled L1 (first-level cache), L2, and L3.

Cache sizes vary. Typically, L1 cache sizes are around 16 kB. In systems with multi-level caches, the upper levels (L2 and L3) are larger than the L1 cache. In many systems, two L1 caches exist in parallel, one for data (D-cache), and one for instructions (I-cache). They typically come together in the L2 cache.

Cache organization

A cache consists of a number of cache lines, organized in sets and ways.

Cache lines

A cache line is typically 32 bits. Every time a miss occurs, the entire cache line is filled from main memory.