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Upgrading & Repairing PCs, Eighth Edition

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Author: Scott Mueller
Retail Price: $49.99
Publisher: Que
ISBN: 0789712954
Publication Date: 9/16/97
Pages: 1168


Chapter 10 - Video Display Hardware

Learn the importance of the monitor and video cards as well as how the two are related

 
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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