Information Technology Reference
In-Depth Information
However, a small area of a computer's main memory may be
predetermined for special purposes. For example, when a computer
first starts up, the computer must have preliminary instructions to
get started. Also, it may be convenient for certain functions to be
wired directly into a section of main memory. This predetermined
memory is called
read-only memory
(
ROM
), and its contents are
built in when a chip is manufactured; instructions can be obtained
from it, but the space cannot be recycled for other uses.
A computer owner might encounter ROM when an added capa
bility requires the owner to plug a special chip application directly
into the machine. Historically, computer software, such as packages
to interpret new computer languages, sometimes was distributed us
ing ROM technology. After buying the new feature, the computer
user opened the machine's cabinet and physically plugged in the
ROM chip.
Today, modern applications for generalpurpose computers typ
ically come on a CD or disk that is not part of main memory, and
usage of ROM is more specialized. One area of application may be
the distribution of operating systems or games for small, specialized
computers. The upgrading of the small computer or the playing of a
new game may require the user to plug a chip into the machine.
A second common use of ROM technology arises behind the
scenes, and a user may not be directly aware of it. For example, op
erating systems, such as Linux, Macintosh OS X, or Windows, are
large programs that are stored on disks or CDs. Although these pro
vide many services, they require a computer to read the disk or CD.
However, when you first turn on a machine, the computer has little
knowledge of what to do. It has not had time to read information
from a disk, and it needs instruction on how to read a disk! Thus,
startup instructions are preprogrammed in ROM. These instruc
tions may include testing some hardware and interacting with a disk
to load the basic elements of Linux, OS X, or Windows. Such work
is possible because the instructions are preprogrammed. Capabilities
may be limited (you do not see a fancy windowbased interface
when you first turn on a computer), but the instructions in ROM al
low the computer to start.
Transitory versus Permanent Memory: Although main (RAM)
memory, cache, and CPU registers handle data relatively quickly,
they cannot remember what they have stored when the power is
