Discuss need of Caches.

Caches are other big thing done in the last 2 decades to enhance performance. Keep things locally when they are going to be used soon. By a physics viewpoint, an access to memory that is almost exclusively off chip will mean signals have to travel which much further in one cycle. Practically, since we do not need to make the system as slow as its slowest element (memory), and the cycle time is not found by the memory access time and quite memory takes some cycles to complete.