Specifications

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Chapter 15 Video Hardware
If you aren’t using a low-emission monitor yet, you can take other steps to protect yourself. The most
important is to stay at arm’s length (about 28 inches) from the front of your monitor. When you move a
couple of feet away, ELF magnetic emission levels usually drop to those of a typical office with fluorescent
lights. Likewise, monitor emissions are weakest at the front of a monitor, so stay at least 3 feet from the
sides and backs of nearby monitors and 5 feet from any photocopiers, which are also strong sources of ELF.
Electromagnetic emissions should not be your only concern; you also should be concerned about
screen glare. In fact, some of the antiglare panels that fit in front of a monitor screen not only reduce
eyestrain, but also cut ELF and VLF emissions.
Note that because plasma and LCD panels don’t use electron guns or magnets, they don’t produce ELF
emissions.
Frequencies
One essential buying decision is to choose a monitor that works with your selected video adapter.
Today, virtually all monitors are multiple-frequency (also called multiscanning and multifrequency)
units that accommodate a range of standards, including those that are not yet standardized. However,
big differences exist in how well various monitors cope with various video adapters.
Tip
High-quality monitors retain their value longer than most other computer components. Although it’s common for a newer,
faster processor to come out right after you have purchased your computer or to find the same model with a bigger hard
disk for the same money, a good quality monitor should outlast your computer. If you purchase a unit with the expectation
that your own personal requirements will grow over the years, you might be able to save money on your next system by
reusing your old monitor.
Some useful features include the following:
■ Front-mounted digital controls that can memorize screen settings
■ Onscreen programmability to enable you to precisely set desired values for screen size and position
■ Self-test mode, which displays a picture even when your monitor is not receiving a signal from the computer
With multiple-frequency CRT monitors, you must match the range of horizontal and vertical frequen-
cies the monitor accepts with those generated by your video adapter. The wider the range of signals,
the more expensive—and more versatile—the monitor. Your video adapter’s vertical and horizontal fre-
quencies must fall within the ranges your monitor supports. The vertical frequency (or refresh/frame
rate) determines the stability of your image (the higher the vertical frequency, the better). Typical verti-
cal frequencies range from 50Hz to 160Hz, but multiple-frequency monitors support different vertical
frequencies at different resolutions. You might find that a bargain monitor has a respectable 120Hz ver-
tical frequency at 640×480 but drops to a less desirable 66Hz at 1280×1024. The horizontal frequency
(or line rate) typically ranges from 31.5KHz to 90KHz or more. By default, most video adapters use a
60Hz default vertical scan frequency to avoid monitor damage.
Although LCD monitors use lower vertical frequencies than CRTs, they avoid problems with screen
flicker because of their design. Because they use transistors to activate all the pixels in the image at
once, as opposed to a scanning electron beam that must work its way from the top to the bottom of
the screen to create an image, LCD panels never flicker.
Refresh Rates (Vertical Scan Frequency)
The refresh rate (also called the vertical scan frequency) is the rate at which the screen display is rewrit-
ten. This is measured in hertz. A refresh rate of 72Hz means that the screen is refreshed 72 times per
second. A refresh rate that is too low causes CRT screens to flicker, contributing to eyestrain. The
higher the refresh rate you use with a CRT display, the better for your eyes and your comfort during
long sessions at the computer.
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