A small-capacity high-speed buffer that holds copies of the most frequently accessed values in computer memory. It is placed between a memory system and its user in order to reduce the effective access time of the memory system. Its performance is based on two assumptions: firstly, small memory is faster than larger memory; secondly, spatial and temporal locality apply to data accesses – if an item of data has just been accessed it will be accessed again soon and data close to it will be more likely to be accessed than data further away.