(^132) PC Hardware: A Beginner’s Guide
of their sockets. Should a ROM chi pcree pout of its socket, it can cause startu p problems.
If you have an older motherboard that includes removable DIP ROM or memory chips,
you should check them occasionally for creep.
CMOS
Because of the initial cost of Complementary Metal Oxide Semiconductor (CMOS) tech-
nology,memory,transistors,andlargepartsofmostmicroprocessorswereoncereserved
for storing the startu pconfiguration of the PC. With technology advances and lower
costs, however, CMOS (pronounced “sea-moss”) technology is now used throughout the
PC. CMOS memory requires only about one-millionth of an am pto hold any data stored
on it. Using only a lithium battery, CMOS memory is able to store the startu pconfigura-
tion of a PC for many years. The term CMOS is still synonymous with the PC’s startup
configuration data.RAM
RAM,orrandom access memory,is used in the PC for its primary memory. RAM is where
all active programs and data are stored so that they are readily available and easily ac-
cessed by the CPU and other components of the PC. When you execute a program on
your PC, a copy of the program is copied into RAM from whatever secondary storage it is
on, usually the hard disk. Once it is in RAM, the instructions that make u pthe program
are passed one at a time to the CPU for execution. Any data the program accepts or reads
from a disk is also stored in RAM.
There are several reasons that RAM is used in a PC, but perhaps the most important is
that RAM can transfer data to and from the CPU much faster than all secondary storage
devices. Without RAM, all programs instructions and data would be read from the disk
drive, slowing the computer to a crawl. With RAM speeds as fast, if not faster, than the
speed of the CPU, the entire PC operates much more efficiently.
RAM is a grou pof integrated circuits (ICsorchips) that contain small electronic com-
ponents (calledcapacitors) that store binary 1s and 0s (see Chapter 2). A variety of mem-
ory chips can be used for RAM, but some are better suited to storing large amounts of
data, fit better in the space available in the PC, and are less expensive. However, not all
memory applications in the PC need to store a large amount of data, so most PCs use
three different layers of memory: primary memory, level 1 (L1) cache, and level 2 (L2)
cache. RAM, in its common usage, refers to the primary memory layer of the PC’s memory.
See Chapter 8 for more information on cache memory.Random Access
Random accessrefers to the ability to access a single storage location in RAM without
touchingthelocationsthatneighborit.Agoodillustrationisthedifferencebetweenacas-
sette tape and a music CD. If you wish to listen to the third song on a cassette tape, you