A computer processor will operate fastest when the data that it wants is in the

A processor works fastest when its wanted data is already in cache memory, the closest and quickest store.

A hard disk is slow secondary storage far from the processor.

An optical disk like a CD or DVD is even slower and used for removable media.

Main memory, the RAM, is faster than disk but slower than cache.

Cache sits on or beside the CPU to cut the time spent fetching data.

The memory hierarchy trades speed for capacity, with cache small but very fast.