Cache memory may even be located on the same electronic chip as the CPU.
Cache is the French word for ???hiding place.??? Cache memory is used to hold a copy of the contents of a small
number of main memory locations. This turns out to be very useful, because program execution demonstrates
a property called ???locality of reference.???
By locality of reference, we mean that for relatively long periods of time, the execution of a program will
reference and affect a small number of memory locations. Accesses to memory are not random. Rather, for one
period of time the program will read and write one part of memory, for example, an array of numbers, and for
another period of time the program will store and retrieve from a different part of memory, for example, a record
from a data base.
When the computer copies the contents of main memory currently being accessed to cache memory, the
CPU can avoid waiting for access to slower main memory, and access the cache instead. Since access times for
cache memory are typically 5 to 10 times faster than access times for main memory, this tactic has proven very
generally effective. Almost all computers built since 1980 have incorporated one or more cache memories in
their design.
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