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.