horizontal and vertical timing signals. Composite
monitors can be either monochrome or color.
RGB (red, green, blue) monitors are color
monitors that use a separate input for each color.
They have greater resolution than the composite video
EGA (Enhanced Graphics Adapter) and V G A
(Video Graphics Array) monitors are RGB monitors
that have even greater resolution. Both EGA and
VGA monitors display sharper characters and
graphics than does the RGB monitor. EGA monitors
can display 43 lines of text instead of the standard 25
lines of the RGB monitor. VGA monitors can display
up to 50 lines of text.
VGA monitors are designed to use analog signals
rather than digital signals to drive the CRT guns.
Digital signals limit the maximum number of colors
that can be displayed to 16. By using variable
(analog) signals to drive the CRT guns, current video
adaptersand monitors are capable of displaying over
256,000 colors. The super VGA and XGA monitors
also use analog signals.
If you are upgrading your
monitor, be sure that the display adapter is compatible
with the new monitor.
Also, there are multiscan or multisync monitors
that can be used with a variety of video cards. These
monitors detect the rate that data is being received and
adjust their scan rates to match the input.
As you can see, the type of monitor you have must
be compatible with the type of video card in the
computer. You can literally burn up a monitor by
plugging it into the wrong type of video card.
Video monitors require very little preventive
maintenance. They should be cleaned periodically to
remove any dust that has collected on the components.
Repair of a failed monitor is difficult because the
monitor diagrams are hard to obtain from the
manufacturer. Also, the price of the repair parts often
exceeds the cost of a new monitor.
VIDEO DISPLAY ADAPTERS
The video display adapter is a circuit card that
plugs into the personal computer to drive the monitor.
Video adapter cards play a major role in how many
colors are displayed and the speed with which
display is updated. Common video adapters are:
MDA (Monochrome Display Adapter)
CGA (Color Graphics Adapter)
EGA (Enhanced Graphics Adapter)
VGA (Video Graphics Array)
SVGA (Super Video Graphics Array)
XGA (Extended Graphics Array)
Monochrome Display Adapter (MDA)
The monochrome display adapter (MDA) was
first display adapter available. It is designed to work
with a monochrome transistor-transistor logic
(TTL) monitor. It is a text-only system that cannot
display graphics or color. The MDA uses a 9 x 14 dot
character box that provides clean sharp characters.
Because most of the software packages developed
today, even word processing and spreadsheets, use
graphics to some extent, the MDA is generally
Color Graphics Adapter (CGA)
The color graphics adapter (CGA) was, at one
time, the most common graphics adapter available. It
supports an RGB monitor with a maximum resolution
of 640 x 200 pixels. The CGA card has two modes of
alphanumeric (A/N) and all points
In both modes, the basic
character set is formed with a resolution of 8 x 8
pixels. The CGA card displays either 40 or 80
columns with 25 lines of text. In the A/N mode, the
CGA card can display up to 16 colors.
The all points addressable mode of operation can
address each pixel individually. The CGA APA mode
supports two resolutions on the screen: medium and
high. The medium resolution is capable of addressing
320 x 200 pixels with 4 colors. The high resolution is