Since the earliest days of microprocessors, system designers have been plagued by a problem in which the speed of the CPU's operation exceeded the bandwidth of the memory subsystem to which it was connected. To avoid wasting CPU cycles while waiting for the memory to fetch the requested data, the universally adopted solution was to use an area of faster (and thus more expensive) memory to cache main memory data. This solution allowed the CPU to operate at its natural speed as long as the data it required was available in the cache.
