RAM (random access memory) is the place in a computer where
application programs, and data in current use are
kept so that they can be quickly reached by the computer's processor.
RAM is much faster to read from and write to than the other
kinds of storage in a computer, the hard disk, floppy disk,
and CD-ROM. However, the data in RAM stays there only as long
as your computer is running. When you turn the computer off,
RAM loses its data. When you turn your computer on again, your
operating system and other files are once again loaded into
RAM can be compared to a person's short-term memory and the
hard disk to the long-term memory. The short-term memory
focuses on work at hand, but can only keep so many facts in
view at one time. If short-term memory fills up, your brain
sometimes is able to refresh it from facts stored in long-term
memory. A computer also works this way. If RAM fills up, the
processor needs to continually go to the hard disk to overlay
old data in RAM with new, slowing down the computer's
operation. Unlike the hard disk which can become completely
full of data so that it won't accept any more, RAM never runs
out of memory. It keeps operating, but much more slowly than
you may want it to.
How Big is RAM?RAM is small, both in physical size
and in the amount of data it can hold. It's much smaller than
your hard disk. A typical computer may come with 256 million
bytes of RAM and a hard disk that can hold 40 billion bytes.
Why Random Access?RAM is called "random access"
because any storage location can be accessed directly.
Originally, the term distinguished regular core memory from
offline memory, usually on magnetic tape in which an item of
data could only be accessed by starting from the beginning of
the tape and finding an address sequentially. Perhaps it
should have been called "nonsequential memory" because RAM
access is hardly random. RAM is organized and controlled in a
way that enables data to be stored and retrieved directly to
specific locations. A term IBM has preferred is direct
access storage or memory. Note that other forms of storage
such as the hard disk and CD-ROM are also accessed directly
(or "randomly") but the term random access is not
applied to these forms of storage.