6 Glossary

chassis
The metal frame to which the electronic components of the computer (such as the
system board, power supply, and drive bays) are attached. The chassis goes inside
the system unit cover.
checksum
A number, ca lc u lated from a b l ock of data, u sed to verify th e integrity of t hat data.
For example, a modem could se n d a block of data and include th e number of 1’s
that occur in the block. The receiving modem could count the number of 1’s it
receives and comp are its o wn number with th e transmi t ted numb er. If t h e number s
are the same, the transmission was probably OK.
clock
Electronic timer (oscillator) used to synchronize computer operations. The
oscillator generates the timing pulses that coordinate and enable the flow of data
within a digital device. Also a circuit powered by battery that keeps track of the
date and time f or human and va r ious system r equirements .
clock speed
The frequency at wh ich a clock osc illates. In microcomput ers, measur ed in MHz.
The fast er the clo ck, the f a ster th e c omputer can comp u te.
CMOS
Complementary Meta l Oxide Semico n du ctor. A chip on t he system boar d t hat
contains nonvolatile memory. CMOS is backed up by an internal lithium battery
that preser v es clock/cal e n dar data and sys tem configur ation par a meters stor ed i n
CMOS.
codec
Coder-decoder. Used primarily with Internet phone and video conferencing
products, t his software c ompresses di gitized dat a and decompres s es it at the ot h er
end, allowi ng f or faster da ta transfer and l ess delays
cold boot
Process of starting up the computer by turning on the power. If power is already on,
the process means to turn off the computer and turn it on again. A cold boot
reinitializ es a ll devices.
compression
Any scheme for recording data with fewer bits. For example, stating how many
times someth ing occurs ca n be shorter t ha n stating eac h occurrenc e. It is shorter t o
say “print a mil lion white pix e ls ” than to say “ print white pix el number one, p rint
white pixel number two . . .”
D
default
The system’s factory setting for a specific device feature or system function. A
setting that a computer uses if it has not been modified by a user.