Specifications
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Chapter 15 Video Hardware
Video Display Technologies
Along with the mouse and keyboard, the video display is a vital part of the user interface of any computer.
Actually, it is a latecomer to computing; before CRT monitors came into general use, the teletypewriter was
the standard computer interface—a large, loud device that printed the input and output characters on a roll
of paper. The first CRT displays used on computers were primitive by today’s standards; they displayed only
text in a single color (usually green), but to users at the time they were a great improvement, allowing real-
time display of input and output data. Over time, color displays were introduced, screen sizes increased, and
LCD technologies moved from the portable computer to the desktop. The latest trends, large-screen plasma
displays and LCD/DLP projectors, reflect the increasing convergence of entertainment and computer tech-
nologies exemplified by developments such as Windows XP Media Center PCs.
Today, PC video displays are much more sophisticated, but you must be careful when selecting video
hardware for your computer. A slow video adapter or monitor can slow down even the fastest and most
powerful PC. Incorrect monitor and video adapter combinations can also cause eyestrain or be unsuit-
able for the tasks you want to accomplish.
The video subsystem of a PC consists of two main components:
■ Monitor (or video display). The monitor can be a CRT or an LCD panel for desktop use, or a wide-
screen LCD TV, plasma display, or projector using LCD or DLP technology.
■ Video adapter (also called the video card or graphics adapter). On many recent low-cost desktop sys-
tems and virtually all portable systems, video might be built into the motherboard or included as
part of this motherboard’s chipset.
This chapter explores the range of PC video adapters on the market today and the displays that work
with them. The remainder of this section covers the various types of display technologies.
Note
The term video, as it is used in this context, does not necessarily imply the existence of a moving image, such as on a
television screen. All adapters that feed signals to a monitor or other display are video adapters, regardless of whether they
are used with applications that display moving images, such as multimedia or videoconferencing software.
How CRT Display Technology Works
A monitor can use one of several display technologies. The original display technology, and still the
most popular, is cathode ray tube (CRT) technology—the same technology used in television sets. CRTs
consist of a vacuum tube enclosed in glass. One end of the tube contains an electron gun assembly that
projects three electron beams, one each for the red, green, and blue phosphors used to create the colors
you see onscreen; the other end contains a screen with a phosphorous coating.
When heated, the electron gun emits a stream of high-speed electrons that are attracted to the other end of
the tube. Along the way, a focus control and deflection coil steer the beam to a specific point on the phos-
phorous screen. When struck by the beam, the phosphor glows. This light is what you see when you watch
TV or look at your computer screen. Three layers of phosphors are used: red, green, and blue. A metal plate
called a shadow mask is used to align the electron beams; it has slots or holes that divide the red, green, and
blue phosphors into groups of three (one of each color). Various types of shadow masks affect picture qual-
ity, and the distance between each group of three (the dot pitch) affects picture sharpness.
◊◊ See “Dot Pitch (CRTs),” p. 884.
Figure 15.1 illustrates the interior of a typical CRT.
The phosphor chemical has a quality called persistence, which indicates how long this glow remains
onscreen. Persistence is what causes a faint image to remain on your TV screen for a few seconds after you
turn off the set. The scanning frequency of the display specifies how often the image is refreshed. You should
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