a supplementary memory system that temporarily stores frequently used instructions and data for quicker processing by the central processor of a computer. The cache augments, and is an extension of, a computer's main memory. Both main memory and cache are internal, random-access memories (RAMs) that use semiconductor-based transistor circuits. Cache holds a copy of only the most frequently used information or program codes stored in the main memory; the smaller capacity of the cache reduces the time required to locate data within it and provide it to the computer for processing.

When a computer's central processor accesses its internal memory, it first checks to see if the information it needs is stored in the cache. If it is, the cache returns the data to the processor. If the information is not in the cache, the processor retrieves it from the main memory. Disk cache memory operates similarly, but the cache is used to hold data that has been recently written on, or retrieved from, a magnetic disk or other external storage device.