Small, fast, hardware-controlled memory that acts as a buffer between a processor and main memory. Cache contains a copy of the most recently used memory locations--addresses and contents--of instructions and data. Every address reference goes first to cache. If the desired instruction or data is not in cache, a cache miss occurs. The contents are fetched across the bus from main memory into the CPU register specified in the instruction being executed and a copy is also written to cache. It is likely that the same location will be used again soon, and, if so, the address is found in cache, resulting in a cache hit. If a write to that address occurs, the hardware not only writes to cache, but can also generate a write-through to main memory.