Program and data are loaded to RAM from secondary storage because the time required to
access a program instruction or piece of data from RAM is significantly less than from
secondary storage. Thousands of instructions or pieces of data can be accessed from RAM
is essentially a high-speed holding area for data and programs. In fact, nothing really
happens in a computer system until the program instructions and data are moved to the
processor. This transfer of instructions and data to the processor can be time-consuming,
even at microsecond speeds. To facilitate an even faster transfer of instructions and add
to the processor, most computers are designed with cache memory. Cache memory is
employed by computer designers to increase the computer system throughput (the
rate at which work is performed). Like RAM, cache is a high-speed holding area for
program instructions and data. However, cache memory uses SRAM (Static RAM)
technology that is about 10 times faster than RAM and about 100 times more expensive.
With only a fraction of the capacity of RAM, cache memory holds only those instructions
and data that are likely to be needed next by the processor. Two types of cache memory
appear widely in computers. The first is referred to as internal cache and is built into
the CPU chip. The second, external cache, is located on chips placed close to the CPU
chip. A computer can have several different levels of cache memory. Level 1 now typically
also built into the CPU like level 1 cache.