Your monitor provides the link between you and your
computer. Although you can possibly get rid of your printer,
disk drives, and expansion cards, you cannot sacrifice the
monitor. Without it, you would be operating blind; you could
not see the results of your calculations or the mistyped words
on-screen.
The first microcomputers were small boxes that lacked
displays. Instead, users observed the information contained in
system registers via banks of flashing LEDs and waited for the
final output to be printed. All interaction with the system
was normally done through a typewriter terminal. When the CRT
(cathode ray tube) terminal or monitor was finally added as an
interface, the computer became more attractive to a wider
audience. This visual trend in user interface technology
continues today with the adoption of graphical user interfaces
such as Windows over text-based systems like DOS.
The video subsystem of a PC consists of two main
components:
- Monitor (or video display)
- Video adapter (also called the video card or graphics
card)
This chapter explores the range of available PC-compatible
video adapters and the displays that work with them.
Monitors
The monitor is, of course, the display located on
top of, near, or inside your computer. Like any computer
device, a monitor requires a source of input. The signals that
run to your monitor come from video circuitry inside or
plugged into your computer. Some computers--such as those that
use the low profile (LPX) or new low profile (NLX) motherboard
form factor--usually contain this circuitry on the
motherboard. Most systems, though, use Baby-AT or ATX style
motherboards and normally incorporate the video on a separate
circuit board that is plugged into an expansion or bus slot.
The expansion cards that produce video signals are called
video cards, video adapters, or graphics
cards. Whether the video circuit is built into the
motherboard or on a separate card, the circuitry operates the
same way and uses generally the same components.
Display Technologies
A monitor may use one of several display technologies. By
far 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; 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 phosphorous screen. When
struck by the beam, the phosphor glows. This light is what you
see when you watch TV or your computer screen.
The phosphor chemical has a quality called
persistence, which indicates how long this glow will
remain on-screen. You should have a good match between
persistence and scanning frequency so that the image has less
flicker (if the persistence is too low) and no ghosts (if the
persistence is too high).
The electron beam moves very quickly, sweeping the screen
from left to right in lines from top to bottom, in a pattern
called a raster. The horizontal scan rate refers
to the speed at which the electron beam moves across the
screen.
During its sweep, the beam strikes the phosphor wherever an
image should appear on- screen. The beam also varies by
intensity in order to produce different levels of brightness.
Because the glow fades almost immediately, the electron beam
must continue to sweep the screen to maintain an image--a
practice called redrawing or refreshing the
screen.
Most displays have an ideal refresh rate (also
called a vertical scan frequency) of about 70 hertz
(Hz), meaning that the screen is refreshed 70 times a second.
Low refresh rates cause the screen to flicker, contributing to
eye strain. The higher the refresh rate, the better for your
eyes.
It is important that the scan rates expected by your
monitor match those produced by your video card. If you have
mismatched rates, you cannot see an image and may actually
damage your monitor.
Some monitors have a fixed refresh rate. Other monitors may
support a range of frequencies; this support provides built-in
compatibility with future video standards (described in the
"Video Cards" section later in this chapter). A monitor that
supports many video standards is called a
multiple-frequency monitor. Most monitors today are
multiple- frequency monitors, which means that they support
operation with a variety of popular video signal standards.
Different vendors call their multiple-frequency monitors by
different names, including multisync, multifrequency,
multiscan, autosynchronous, and autotracking.
Phosphor-based screens come in two styles--curved
and flat. The typical display screen is curved, meaning
that it bulges outward from the middle of the screen. This
design is consistent with the vast majority of CRT designs
(the same as the tube in your television set).
The traditional screen is curved both vertically and
horizontally. Some models use the Trinitron design,
which is curved only horizontally and is flat vertically. Many
people prefer this flatter screen because it results in less
glare and a higher-quality, more accurate image. The
disadvantage is that the technology required to produce
flat-screen displays is more expensive, resulting in higher
prices for the monitors.
Alternative display designs are available. Borrowing
technology from laptop manufacturers, some companies provide
LCD (liquid-crystal display) displays. LCDs have low-glare
flat screens and low power requirements (5 watts versus nearly
100 watts for an ordinary monitor). The color quality of an
active-matrix LCD panel actually exceeds that of most CRT
displays. At this point, however, LCD screens usually are more
limited in resolution than typical CRTs and are much more
expensive; for example, a 12.1-inch screen costs several
thousand dollars. There are three basic LCD choices:
passive-matrix monochrome, passive-matrix color, and
active-matrix color. The passive-matrix designs are also
available in single- and dual-scan versions.
In an LCD, a polarizing filter creates two separate light
waves. In a color LCD, there is an additional filter that has
three cells per each pixel--one each for displaying red,
green, and blue.
The light wave passes through a liquid-crystal cell, with
each color segment having its own cell. The liquid crystals
are rod-shaped molecules that flow like a liquid. They enable
light to pass straight through, but an electrical charge
alters their orientation, as well as the orientation of light
passing through them. Although monochrome LCDs do not have
color filters, they can have multiple cells per pixel for
controlling shades of gray.
In a passive-matrix LCD, each cell is controlled by
electrical charges transmitted by transistors according to row
and column positions on the screen's edge. As the cell reacts
to the pulsing charge, it twists the light wave, with stronger
charges twisting the light wave more. Supertwist refers
to the orientation of the liquid crystals, comparing on mode
to off mode--the greater the twist, the higher the
contrast.
Charges in passive-matrix LCDs are pulsed, so the displays
lack the brilliance of active-matrix, which provides a
constant charge to each cell. To increase the brilliance, some
vendors have turned to a new technique called double-scan
LCD, which splits passive-matrix screens into a top half
and bottom half, cutting the time between each pulse. Besides
increasing the brightness, dual-scan designs also increase the
response time or speed of the display, making this type more
usable for video or other applications where the displayed
information changes rapidly.
In an active-matrix LCD, each cell has its own transistor
to charge it and twist the light wave. This provides a
brighter image than passive-matrix displays because the cell
can maintain a constant, rather than momentary, charge.
However, active-matrix technology uses more energy than
passive-matrix. With a dedicated transistor for every cell,
active-matrix displays are more difficult and expensive to
produce.
In both active- and passive-matrix LCDs, the second
polarizing filter controls how much light passes through each
cell. Cells twist the wavelength of light to closely match the
filter's allowable wavelength. The more light that passes
through the filter at each cell, the brighter the pixel.
Monochrome LCDs achieve gray scales (up to 64) by varying
the brightness of a cell or dithering cells in an on-and-off
pattern. Color LCDs, on the other hand, dither the three-color
cells and control their brilliance to achieve different colors
on the screen. Double-scan passive-matrix LCDs have recently
gained in popularity because they approach the quality of
active-matrix displays but do not cost much more to produce
than other passive-matrix displays.
The big problem with active-matrix LCDs is that the
manufacturing yields are low, forcing higher prices. This
means that many of the panels produced have more than a
certain maximum number of failed transistors. The resulting
low yields limit the production capacity and incur higher
prices.
In the past, several hot CRTs were needed to light an LCD
screen, but portable computer manufacturers now use a single
tube the size of a cigarette. Light emitted from a tube gets
spread evenly across an entire display using fiber-optic
technology.
Thanks to supertwist and triple-supertwist LCDs, today's
screens enable you to see the screen clearly from more angles
with better contrast and lighting. To improve readability,
especially in dim light, some laptops include
backlighting or edgelighting (also called
sidelighting). Backlit screens provide light from a
panel behind the LCD. Edgelit screens get their light from the
small fluorescent tubes mounted along the sides of the screen.
Some older laptops excluded such lighting systems to lengthen
battery life. Most modern laptops enable you to run the
backlight at a reduced power setting that dims the display but
allows for longer battery life.
The best color displays are active-matrix or
thin-film transistor (TFT) panels, in which each pixel
is controlled by three transistors (for red, green, and blue).
Active-matrix-screen refreshes and redraws are immediate and
accurate, with much less ghosting and blurring than in
passive-matrix LCDs (which control pixels via rows and columns
of transistors along the edges of the screen). Active-matrix
displays are also much brighter and can easily be read at an
angle.
An alternative to LCD screens is gas-plasma technology,
typically known for its black and orange screens in some of
the older Toshiba notebook computers. Some companies are
incorporating gas-plasma technology for desktop screens and
possibly color high-definition television (HDTV) flat-panel
screens.
Monochrome versus Color
During the early years of the IBM PC and compatibles,
owners had only two video choices--color using a CGA display
adapter and monochrome using an MDA display adapter. Since
then, many adapter and display options have hit the
market.
Monochrome monitors produce images of one color. The most
popular is amber, followed by white and green. The color of
the monitor is determined by the color of the phosphors on the
CRT screen. Some monochrome monitors with white phosphors can
support many shades of gray.
Color monitors use more sophisticated technology than
monochrome monitors, which accounts for their higher prices.
Whereas a monochrome picture tube contains one electron gun, a
color tube contains three guns arranged in a triangular shape
referred to as a delta configuration. Instead of amber,
white, or green phosphors, the monitor screen contains
phosphor triads, which consist of one red phosphor, one green
phosphor, and one blue phosphor arranged in the same pattern
as the electron guns. These three primary colors can be mixed
to produce all other colors.
The Right Size
Monitors come in different sizes, ranging from 9-inch to
42-inch diagonal measure. The larger the monitor, the higher
the price tag. The most common monitor sizes are 14, 15, 17,
and 21 inches. These diagonal measurements, unfortunately,
represent not the actual screen that will be displayed but the
size of the tube. As a result, comparing one com-pany's
15-inch monitor to that of another may be unfair unless you
actually measure the active screen area. This area can vary
slightly from monitor to monitor, so one com-pany's 17-inch
monitor may display a 15.0-inch image, and another company's
17-inch monitor may present a 15.5-inch image.
The following table shows the advertised monitor diagonal
size along with the approximate diagonal measure of the actual
active viewing area for the most common display sizes:
Monitor Size (in Inches) |
Viewing Area (in Inches) |
12 |
10.5 |
14 |
12.5 |
15 |
13.5 |
16 |
14.5 |
17 |
15.5 |
18 |
16.5 |
19 |
17.5 |
20 |
18.5 |
21 |
19.5 |
The size of the actual viewable area varies slightly from
manufacturer to manufacturer, but these figures are
representative of most monitors. As you can see, the viewable
area of a monitor is normally about 1.5 inches less than the
advertised specification. The viewing area refers to the
diagonal measure of the lighted area on the screen. In other
words, if you are running Windows, the viewing area is the
actual diagonal measure of the desktop.
In most cases, the 17-inch monitor is currently the best
bargain in the industry. A 17-inch monitor is most often
recommended for new systems and is not much more expensive
than a 15-inch display. I recommend a 17-inch monitor as the
minimum you should consider for most normal applications.
Low-end applications can still get away with a 15-inch
display, but resolution will suffer. 18- to 21-inch or larger
displays are recommended for high-end systems, especially
where graphics applications are the major focus.
Larger monitors are handy for applications such as desktop
publishing, in which the smallest details must be clearly
visible. With a 17-inch or larger display, you can see nearly
an entire 8 1/2x11-inch page in 100 percent view--in other
words, what you see on-screen virtually matches the page that
will be printed. This feature is called WYSIWYG--short
for "what you see is what you get." If you can see the entire
page at its actual size, you can save yourself the trouble of
printing several drafts before you get it right.
With the popularity of the Internet, monitor size and
resolution becomes even more of an issue. Many Web pages are
being designed for 1,024x768 resolution, which requires a
17-inch CRT display as a minimum to handle without eye strain
and inadequate focus. Because of their much tighter dot pitch,
LCD displays in laptop computers can handle that resolution
easily on 13.3- or even 12.1-inch displays. Using 1,024x768
resolution means you will be able to view most Web pages
without scrolling sideways, which is a major convenience.
Monitor Resolution
Resolution is the amount of detail that a monitor
can render. This quantity is expressed in the number of
horizontal and vertical picture elements, or pixels,
contained in the screen. The greater the number of pixels, the
more detailed the images. The resolution required depends on
the application. Character-based applications (such as word
processing) require little resolution, whereas
graphics-intensive applications (such as desktop publishing
and Windows software) require a great deal.
There are several standard resolutions available in PC
graphics adapters. The following table lists the standard
resolutions used in PC video adapters and the term used to
commonly describe them:
Resolution |
Acronym |
Standard Designation |
640x480 |
VGA |
Video Graphics Array |
800x600 |
SVGA |
Super VGA |
1,024x768 |
XGA |
eXtended Graphics Array |
1,280x1,024 |
UVGA |
Ultra VGA |
In a monochrome monitor, the picture element is a screen
phosphor, but in a color monitor, the picture element is a
phosphor triad. This difference raises another consideration
called dot pitch, which applies only to color monitors.
Dot pitch is the distance, in millimeters, between phosphor
triads. Screens with a small dot pitch contain less distance
between the phosphor triads; as a result, the picture elements
are closer together, producing a sharper picture. Conversely,
screens with a large dot pitch tend to produce images that are
less clear.
Another consideration of resolution is the dot pitch of the
monitor. Smaller pitch values allow the monitor to produce
sharper images. The original IBM PC color monitor had a dot
pitch of 0.43mm, which is considered to be poor by almost any
standard. The state-of-the-art displays marketed today have a
dot pitch of 0.25mm or less; I would not recommend more than
0.28mm in most cases. While you can save money by picking a
smaller monitor or one with a higher dot pitch, the trade-off
is not usually worth it.
Interlaced versus Noninterlaced
Monitors and video adapters may support interlaced or
noninterlaced resolution. In noninterlaced
(conventional) mode, the electron beam sweeps the screen
in lines from top to bottom, one line after the other,
completing the screen in one pass. In interlaced mode,
the electron beam also sweeps the screen from top to bottom,
but it does so in two passes--sweeping the odd lines first and
the even lines second. Each pass takes half the time of a full
pass in noninterlaced mode. Therefore, both modes refresh the
entire screen in the same amount of time. This technique
redraws the screen faster and provides more stable images.
Monitors that use interlacing can use lower refresh rates,
lessening their cost. The drawback is that interlacing depends
on the ability of the eye to combine two nearly identical
lines, separated by a gap, into one solid line. If you are
looking for high-quality video, however, you want to get a
video adapter and monitor that support high-resolution,
noninterlaced displays.
Energy and Safety
A properly selected monitor can save energy. Many PC
manufacturers are trying to meet the Environmental Protection
Agency's Energy Star requirements. Any PC-and-monitor
combination that consumes less than 60 watts (30 watts apiece)
during idle periods can use the Energy Star logo. Some
research shows that such "green" PCs can save each user about
$70 per year in electricity costs.
Monitors, being one of the most power-hungry computer
components, can contribute to those savings. Perhaps the
best-known energy-saving standard for monitors is VESA's
Display Power-Management Signaling (DPMS) spec, which defines
the signals that a computer sends to a monitor to indicate
idle times. The computer or video card decides when to send
these signals.
If you buy a DPMS monitor, you can take advantage of energy
savings without remodeling your entire system. If you do not
have a DPMS-compatible video adapter, some cards can be
upgraded to DPMS with a software utility typically available
at no cost. Similarly, some energy-saving monitors include
software that works with almost any graphics card to supply
DPMS signals.
Another trend in green monitor design is to minimize the
user's exposure to potentially harmful electromagnetic fields.
Several medical studies indicate that these electromagnetic
emissions may cause health problems, such as miscarriages,
birth defects, and cancer. The risk may be low, but if you
spend a third of your day (or more) in front of a computer
monitor, that risk is increased.
The concern is that VLF (very low frequency) and ELF
(extremely low frequency) emissions might affect the body.
These two emissions come in two forms: electric and
magnetic. Some research indicates that ELF magnetic
emissions are more threatening than VLF emissions, because
they interact with the natural electric activity of body
cells. Monitors are not the only culprits; significant ELF
emissions also come from electric blankets and power lines.
NOTE: ELF and VLF are a form of
electromagnetic radiation; they consist of radio frequencies
below those used for normal radio broadcasting.
These two frequencies are covered by the new Swedish
monitor-emission standard called SWEDAC, named after
the Swedish regulatory agency. In many European countries,
government agencies and businesses buy only low-emission
monitors. The degree to which emissions are reduced varies
from monitor to monitor. The Swedish government's MPR I
standard, which dates back to 1987, is the least restrictive.
MPR II, established in 1990, is significantly stronger (adding
maximums for ELF as well as VLF emissions) and is the level
that you will most likely find in low-emission monitors
today.
A more stringent 1992 standard called TCO further
tightens the MPR II requirements. In addition, it is a more
broad-based environmental standard that includes power-saving
requirements and emission limits. Nanao is one of the few
manufacturers currently offering monitors that meet the TCO
standard.
A low-emission monitor costs about $20 to $100 more than
similar regular-emission monitors. When you shop for a
low-emission monitor, don't just ask for a low-emission
monitor; also find out whether the monitor limits specific
types of emission. Use as your guideline the three
electromagnetic-emission standards described in this
section.
If you decide not to buy a low-emission monitor, 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
antiglare screens not only reduce eye strain but also cut ELF
and VLF emissions.
Monitor Buying Criteria
A monitor may account for as much as 50 percent of the
price of a computer system. What should you look for when you
shop for a monitor?
The trick is to pick a monitor that works with your
selected video card. You can save money by purchasing a
single-standard (fixed-frequency) monitor and a matching video
card; for example, you can order a VGA monitor and a VGA video
card. For greatest flexibility, get a multisync monitor that
accommodates a range of standards, including those that are
not yet standardized.
With multisync monitors, you must match the range of
horizontal and vertical frequencies the monitor accepts with
those generated by your video card. The wider the range of
signals, the more expensive--and more versatile--the monitor.
Your video card's vertical and horizontal frequencies must
fall within the ranges supported by your monitor. The
vertical frequency (or refresh/frame rate) determines
how stable your image will be. The higher the vertical
frequency, the better. Typical vertical frequencies range from
50 to 90Hz. The horizontal frequency (or line rate)
ranges between 31.5KHz to 60KHz or more.
To keep the horizontal frequency low, some video cards use
interlaced signals, alternately displaying half the lines of
the total image. On most monitors, interlacing produces a
pronounced flicker in the display, unless the phosphor is
designed with a very long persistence. For this reason, you
should avoid using interlaced video modes if possible. Some
older cards and displays used interlacing as an inexpensive
way to attain a higher resolution than otherwise would be
possible. For example, the original IBM XGA adapters and
monitors used an interlaced vertical frame rate of 43.5Hz in
1,024x768 mode, instead of the 60Hz or higher frame rate that
most other adapters and displays use at that resolution.
In my experience, a 60Hz vertical scan frequency (frame
rate) is the minimum anybody should use, and even at this
frequency a flicker will be noticed by most people. Especially
on a larger display, this can cause eye strain and fatigue. If
you can select a frame rate (vertical scan frequency) of 72Hz
or higher, most people will not be able to discern any
flicker. Most modern displays easily handle vertical
frequencies of up to 85Hz or more, which greatly reduces the
flicker seen by the user. Note that increasing the frame rate
can slow down the video hardware, because it now needs to
display each image more times per second. In general, I
recommend you set the lowest frame rate you are comfortable
with.
When you shop for a VGA monitor, make sure that the monitor
supports a horizontal frequency of at least 31.5KHz--the
minimum that a VGA card needs to paint a 640x480 screen. The
VESA Super VGA (800x600) or SVGA standard requires a 72Hz
vertical frequency and a horizontal frequency of at least
48KHz. The sharper 1,024x768 image requires a vertical
frequency of 60Hz and a horizontal frequency of 58KHz. If the
vertical frequency increases to 72Hz, the horizontal frequency
must be 58KHz. For a super-crisp display, look for available
vertical frequencies of 75Hz or higher and horizontal
frequencies of up to 90KHz or more.
Most of the analog monitors produced today are, to one
extent or another, multisync. Because literally hundreds of
manufacturers produce thousands of monitor models, it is
impractical to discuss the technical aspects of each monitor
model in detail. Suffice it to say that before investing in a
monitor, you should check the technical specifications to make
sure that the monitor meets your needs. If you are looking for
a place to start, check out some of the different magazines,
which periodically feature reviews of monitors. If you cannot
wait for a magazine review, investigate monitors at the Web
sites run by any of the following vendors:
IBM |
Sony |
NEC |
Mitsubishi |
Viewsonic |
|
Each of these manufacturers creates monitors that set the
standards by which other monitors can be judged. Although you
typically pay a bit more for these manufacturers' monitors,
they offer a known high level of quality and compatibility as
well as service and support.
Many inexpensive monitors are curved because it is easier
to send an electron beam across them. Flat-screen monitors,
which are a bit more expensive, look better to most people. As
a general rule, the less curvature a monitor has, the less
glare it will reflect.
Consider the size of your desk before you think about a
monitor 16 inches or larger. A 16-inch monitor typically is at
least 1 1/2 feet deep, and a 20-inch monitor takes up 2 square
feet. Typical 14-inch monitors are 16 to 18 inches deep.
You also should check the dot pitch of the monitor. Smaller
pitch values indicate sharper images. Most monitors have a dot
pitch between 0.25 and 0.52mm. To avoid grainy images, look
for a dot pitch of 0.26mm or smaller. Be wary of monitors with
anything larger than a 0.28mm dot pitch; they lack clarity for
fine text and graphics.
What resolution do you want for your display? Generally,
the higher the resolution, the larger the display you will
want. If you are operating at 640x480 resolution, for example,
you should find a 15-inch monitor to be comfortable. At
1,024x768, you probably will find that the display of a
15-inch monitor is too small and therefore will prefer to use
a larger one, such as a 17-inch monitor.
Here are the minimum monitor sizes I recommend to properly
display popular VGA and SVGA resolutions:
Resolution |
Minimum Recommended Monitor |
640x480 |
13-inch |
800x600 |
15-inch |
1,024x768 |
17-inch |
1,280x1,024 |
21-inch |
The minimum recommended display size is the advertised
diagonal display dimension of the monitor. Note that this is
not what the monitor may be capable of, but is what I
recommend. In other words, most 15-inch monitors will display
resolutions at least up to 1,024x768, but the characters,
icons, and displayed information will be too small and will
cause eye strain if you try to run beyond the 800x600
recommended. In other words, if you plan on spending a lot of
time in front of your PC, and you want to run 1,024x768
resolution, I absolutely recommend a 17-inch display. Anything
smaller is not considered proper ergonomics, and eye strain,
headaches, and fatigue can result.
One exception to this rule is with the laptop and notebook
displays. These are usually an LCD-type display, which is
always crisp and perfectly focused by nature. Also, the
dimensions advertised for the LCD screens are exactly what you
get for display, unlike conventional CRT-based monitors. So
the 12.1-inch LCD panels found on many laptop systems today
actually have a viewable area that is 12.1-inch diagonal. In
other words, 12.1-inch is the size of the Windows desktop or
functional area of the screen. This measurement compares to a
14-inch or even 15-inch conventional display in most cases.
Not only that, but the LCD is so crisp that you can easily
handle resolutions that are higher than otherwise would be
acceptable on a CRT. For example, many of the high-end laptop
systems now use 13.3-inch LCD panels that feature 1,024x768
resolution. Although this resolution is unacceptable on a
14-inch or 15-inch CRT display, it works well on the 13.3-inch
LCD panel due to the crystal clear image.
TIP: Get a monitor with positioning and image
controls that are easy to reach. Look for more than just
basic contrast and brightness controls; some monitors also
enable you to adjust the width and height of your screen
images. A tilt-swivel stand should be included with your
monitor, enabling you to move the monitor to the best angle
for your use.
Most of the newer monitors now use digital controls instead
of analog controls. This has nothing to do with the signals
sent to the monitor, but the controls (or lack of them) on the
front panel. Monitors with digital controls have a built-in
menu system that allows you to set things like brightness,
contrast, screen size, vertical and horizontal shifts, and
even focus. The menu is brought up on the screen by a button,
and you use controls to make menu selections and vary the
settings. When completed, the monitor saves your settings in
NVRAM (Non-Volatile RAM) in the monitor. These settings are
permanently stored using no battery, and can be altered at any
time in the future. Digital controls give a much higher level
of control over the monitor, and are highly recommended.
A monitor is such an important part of your computer that
it is not enough to know just its technical specifications.
Knowing a monitor has a 0.28mm dot pitch does not necessarily
tell you that it is ideal for you. It is best to "kick the
tires" of your new monitor at a showroom or (with a liberal
return policy) in the privacy of your office. To test your
monitor:
- Draw a circle with a graphics program. If the result is
an oval, not a circle, this monitor will not serve you well
with graphics or design software.
- Type some words in 8- or 10-point type (1 point equals
1/72 inch). If the words are fuzzy, or if the black
characters are fringed with color, select another
monitor.
- Turn the brightness up and down while examining the
corner of the screen's image. If the image blooms or swells,
it is likely to lose focus at high brightness
levels.
- Load Microsoft Windows to check for uniform focus. Ar re
the corner icons as sharp as the rest of the screen? Are the
lines in the title bar curved or wavy? Monitors usually are
sharply focused at the center, but seriously blurred corners
indicate a poor design. Bowed lines may be the result of a
poor graphics card, so don't dismiss a monitor that shows
those lines without using another card to double-check the
effect.
- A good monitor will be calibrated so that rays of red,
green, and blue light hit their targets (individual phosphor
dots) precisely. If they don't, you have bad convergence.
This is apparent when edges of lines appear to illuminate
with a specific color. If you have good convergence, the
colors will be crisp, clear, and true, provided that there
is not a predominant tint in the phosphor.
Video Cards
A video card provides signals that operate your
monitor. With the PS/2 systems introduced in 1987, IBM
developed new video standards that have overtaken the older
display standards in popularity and support.
Most video cards follow one of several industry
standards:
MDA (Monochrome Display Adapter) |
VGA (Video Graphics Array) |
CGA (Color Graphics Adapter) |
SVGA (Super VGA) |
EGA (Enhanced Graphics Adapter) |
XGA (eXtended Graphics
Array) |
These adapters and video standards are supported by
virtually every program that runs on IBM or compatible
equipment. Other systems are developing into de facto
standards as well. For example, SVGA offers different
resolutions from different vendors, but 1,024x768 resolution
is becoming a standard resolution for doing detailed work.
Most microcomputer monitors support at least one video
standard, enabling you to operate them with video cards and
software that are compatible with that standard. For example,
a monitor that supports VGA may operate with VGA video cards
and VGA software.
Obsolete Display Adapters
Although many types of display systems are considered to be
standards, not all systems are considered to be viable
standards for today's hardware and software. For example, the
CGA standard works but is unacceptable for running the
graphics-intensive programs on which many users rely. In fact,
Microsoft Windows 3.1 does not work with any PC that has
less-than-EGA resolution, and Windows 95 and Windows NT
require VGA as an absolute minimum. The next several sections
discuss the display adapters that are viewed as being obsolete
in today's market.
Monochrome Display Adapter (MDA) and Display
The simplest (and first available) display type is the IBM
Monochrome Display Adapter (MDA). It was introduced
along with the IBM PC itself in 1981. The MDA video card can
display text only at a 720x350 resolution. One interesting
point is that the MDA card also incorporated a printer port
and was the first multi-function adapter card available. A
character-only system, the display has no inherent graphics
capabilities. The display originally was a top-selling option
because it is fairly cost-effective. As a bonus, the MDA
provides a printer interface, conserving an expansion
slot.
The display is known for clarity and high resolution,
making it ideal for business use--especially for businesses
that use DOS-based word processing or spreadsheet
programs.
Figure 10.1 shows the MDA pinouts.
FIG.
10.1 Monochrome Display Adapter
pinouts.
Because the monochrome display is a character-only display,
you cannot use it with software that requires graphics.
Originally, that drawback only kept the user from playing
games on a monochrome display, but today even the most serious
business software uses graphics and color to great advantage.
With the 9x14 dot character box (matrix), the IBM
monochrome monitor displays attractive characters.
Table 10.1 summarizes the features of the MDA's single mode
of operation.
Table 10.1 IBM Monochrome Display Adapter (MDA)
Specifications
Resolution |
Colors |
Mode Type |
BIOS Mode |
Character Format |
Character Box |
Vertical (Hz) |
Horizontal (KHz) |
720x350 |
4 |
Text |
07h |
80x25 |
9x14 |
50 |
18.432 |
Later, a company named Hercules released a video card
called the Hercules Graphics Card (HGC). This card
displays sharper text and can handle graphics, such as bar
charts.
Color Graphics Adapter (CGA) and Display
The Color Graphics Adapter (CGA) was introduced
along with the IBM PC itself in 1981 and for many years was
the most common video card. Of course, by today's standards,
its capabilities now leave much to be desired. This adapter
has two basic modes of operation: alphanumeric (A/N) or all
points addressable (APA). In A/N mode, the card
operates in 40-column by 25-line mode or 80-column by 25-line
mode with 16 colors. In APA and A/N modes, the character set
is formed with a resolution of 8x8 pixels. In APA mode,
two resolutions are available: medium-resolution color mode
(320x200), with four colors available from a palette of 16;
and two-color high-resolution mode (640x200). Figures 10.2 and
10.3 show the pinouts for the CGA.
Most of the monitors sold for the CGA are RGBs, not
composite monitors. The color signal of a composite monitor
contains a mixture of colors that must be decoded or
separated. RGB monitors receive red, green, and blue
separately, and combine the colors in different proportions to
generate other colors. RGB monitors offer better resolution
than composite monitors, and they do a much better job of
displaying 80-column text.
One drawback of a CGA video card is the fact that it
produces flicker and snow. Flicker is the annoying
tendency of the text to flash as you move the image up or
down. Snow is the flurry of bright dots that can appear
anywhere on the screen.
Most companies that sold CGA-type adapters have long since
discontinued those products. When many VGA cards cost less
than $100, recommending a CGA makes little sense.
Table 10.2 lists the specifications for all CGA modes of
operation.
Table 10.2 IBM Color Graphics Adapter (CGA)
Specifications
Resolution |
Colors |
Mode Type |
BIOS Mode |
Character Format |
Character Box |
Vertical (Hz) |
Horizontal (KHz) |
320x200 |
16 |
Text |
00/01h |
40x25 |
8x8 |
60 |
15.75 |
640x200 |
16 |
Text |
02/03h |
80x25 |
8x8 |
60 |
15.75 |
160x200 |
16 |
APA |
-- |
-- |
-- |
60 |
15.75 |
320x200 |
4 |
APA |
04/05h |
40x25 |
8x8 |
60 |
15.75 |
640x200 |
2 |
APA |
06h |
80x25 |
8x8 |
60 |
15.75 | APA = All
points addressable (graphics) -- = Not supported
FIG.
10.2 CGA display connector
specifications.
FIG.
10.3 CGA RF modulator and
light-pen connector specifications.
Enhanced Graphics Adapter (EGA) and Display
The IBM Enhanced Graphics Adapter was introduced in
1984, just after the IBM AT system. It was discontinued when
the PS/2 systems were introduced in April 1987. It consists of
a graphics board, a graphics memory-expansion board, a
graphics memory-module kit, and a high-resolution color
monitor. The whole package originally cost about $1,800! The
aftermarket gave IBM a great deal of competition in this area;
it was possible to put together a similar system from non-IBM
vendors for much less money. One advantage of EGA, however, is
that you can build your system in modular steps. Because the
card works with any of the monitors IBM produced at the time,
you can use it with the IBM Monochrome Display, the earlier
IBM Color Display, or the IBM Enhanced Color Display.
With the EGA card, the IBM color monitor displays 16 colors
in 320x200 or 640x200 mode, and the IBM monochrome monitor
shows a resolution of 640x350 with a 9x14 character box (text
mode).
Figures 10.4 and 10.5 show the pinouts and P-2 connector of
the EGA.
FIG.
10.4 EGA display connector
specifications.
FIG.
10.5 EGA light-pen connector
specifications.
With the EGA card, the IBM Enhanced Color Display is
capable of displaying 640x350 pixels in 16 colors from a
palette of 64. The character box for text is 8x14, compared
with 8x8 for the earlier CGA board and monitor. The 8x8
character box can be used, however, to display 43 lines of
text. Through software, the character box can be manipulated
up to the size of 8x32.
You can enlarge a RAM-resident, 256-member character set to
512 characters by using the IBM memory expansion card. A
1,024-character set is added with the IBM graphics
memory-module kit. These character sets are loaded from
programs.
All this memory fits in the unused space between the end of
RAM user memory and the current display-adapter memory. The
EGA has a maximum 128K of memory that maps into the RAM space
just above the 640K boundary. If you install more than 640K,
you will probably lose the extra memory after installing the
EGA. The graphics memory-expansion card adds 64K to the
standard 64K, for a total 128K. The IBM graphics memory-module
kit adds another 128K, for a total 256K. This second 128K of
memory is only on the card and does not consume any of the
PC's memory space. (Because almost every aftermarket EGA card
comes configured with the full 256K of memory, expansion
options are not necessary.)
The VGA system supersedes the EGA in many respects. The EGA
has problems emulating the earlier CGA or MDA adapters, and
some software that works with the earlier cards will not run
on the EGA until the programs are modified.
Table 10.3 shows the modes supported by the EGA adapter.
Table 10.3 IBM Enhanced Graphics Adapter (EGA)
Specifications
Resolution |
Colors |
Mode Type |
BIOS Mode |
Character Format |
Character Box |
Vertical (Hz) |
Horizontal (KHz) |
320x350 |
16 |
Text |
00/01h |
40x25 |
8x14 |
60 |
21.85 |
640x350 |
16 |
Text |
02/03h |
80x25 |
8x14 |
60 |
21.85 |
720x350 |
4 |
Text |
07h |
80x25 |
9x14 |
50 |
18.432 |
320x200 |
16 |
APA |
0Dh |
40x25 |
8x8 |
60 |
15.75 |
640x200 |
16 |
APA |
0Eh |
80x25 |
8x8 |
60 |
15.75 |
640x350 |
4 |
APA |
0Fh |
80x25 |
8x14 |
50 |
18.432 |
640x350 |
16 |
APA |
10h |
80x25 |
8x14 |
60 |
21.85 |
APA = All points addressable (graphics)
Professional Color Display and Adapter
The Professional Graphics Display System is a video
display product that IBM introduced in 1984. At $4,290, the
system was too expensive to become a mainstream product and
never achieved any popularity. It was the first
processor-based video adapter for PCs; it actually
incorporated an 8088 processor on the card itself.
The system consists of a Professional Graphics Monitor and
a Professional Graphics Card Set. When fully expanded, this
card set uses three slots in an XT or AT system--a high price
to pay, but the features are impressive. The Professional
Graphics Adapter (PGA) offers three-dimensional rotation and
clipping as a built-in hardware function. The adapter can run
60 frames of animation per second because the PGA uses a
built-in dedicated microcomputer.
The Professional Graphics card and monitor targeted
engineering and scientific applications rather than financial
or business applications. This system, which was discontinued
when the PS/2 was introduced, has been replaced by the VGA and
other higher-resolution graphics standards for these newer
systems.
Table 10.4 lists all supported PGA modes.
Table 10.4 IBM Professional
Graphi |