ABSTRACT
Since the advent of microprocessors, the clock speeds of CPUs have increased at an exponential rate. While the speed at which off-chip memory can be accessed has also increased exponentially, it has not increased at the same rate. A memory hierarchy is used to bridge this gap between the speeds of the CPU and the memory. In a memory hierarchy, the off-chip main memory is at the bottom. Above it, one or more levels of memory reside. Each level is faster than the level below it but stores a smaller amount of data. Sometimes registers are considered to be the topmost level of this hierarchy.
