Classic Computer Magazine Archive COMPUTE! ISSUE 156 / SEPTEMBER 1993 / PAGE 8

Seeing is believing: what you should know about your computer's display system. (includes related articles)
by William Harrel

What you should know about your

computer"s display system

Have you ever wondered why Windows looks so different on your monitor from the way it looks on the monitor at the computer store? Or why your friend Joe's fonts appear so much crisper and clearer? Or how come his colors are so plentiful and pure and his graphics display is so much faster? The answer is simple. Like cars, washing machines, and lawn mowers, computer display systems come with a variety of options, and, of course, in a wide range of prices.

Since the introduction of Windows 3.0, with its support of high resolutions and 16.7 million colors, hardware vendors have been scrambling to find ways to make what shows up on your monitor faster and prettier. While the results are impressive - never before have type and graphics displayed so well on so many computer screens - the resulting plethora of display system types and sizes has become mind-boggling. You have 8-bit, 16-bit, and 24-bit color displaying at four or five different resolutions; graphics accelerators; local-bus adapters; analog and digital video; VGA and Super VGA - no wonder it's so confusing!

Let's see if we can't make it all make sense.

Your Display System

To display information, be it text or graphics, all computers require two components: a display adapter and a monitor. Display systems run in various modes providing different palettes and resolutions. Keep in mind during this discussion that for you to get the most from a display system, your display adapter and monitor must support the same modes. It does you liftle good, for example, to spend the extra money on a Super VGA display adapter if your monitor supports only VGA.

Pick a Card

Often called a graphics card, the display adapter is usually a separate card that slips into a bus slot on the motherboard (some computers have display adapters built onto the motherboard). The display adapter processes information from the computer and sends it to the monitor.

When looking for a graphics card, you should consider the resolution, number of colors (or bits per pixel), the screen refresh rate, and whether it supports interlaced or noninterlaced display. Also determine whether the card is accelerated. (Accelerated cards are discussed in the accompanying sidebar "Running Windows at the Speed of Light.")


Resolution refers to the number of dots, or pixels, on the screen. The higher the resolution, the more information you can fit on the screen. In Windows that means that you can view more open windows at the same time, or, in a desktop publishing program, such as PageMaker, you get a better what-you-see-is- what-you-get (WYSIWYG) representation of how the page will print.

Standard VGA has a resolution of 640 pixels across and 480 pixels down (640 x 480). Super VGA mode is 800 x 600 or higher. VGA and Super VGA are the most common resolutions, but 1024 x 768 and even 1280 x 1024 (sometimes called Ultra or Extended VGA) are becoming increasingly popular.

When you choose a resolution, you'll also need to consider the screen size of the monitor. If you cram too many pixels onto a 14-inch monitor, text becomes too small to be read easily. A good rule of thumb is to use a system that approximates the size of the final printed text. This table should help you match resolution and monitor sizes. Resolution Screen Size VGA (640 x 480) 14 inches Super VGA 15-16inches

(800 x 600) Extended VGA 17 inches or (1 024 x 768) higher (1 280 x 1024) 19-21 inches

Keep in mind that these resolution recommendations are helpful for viewing text. However, no matter what size your monitor, graphics applications benefit greatly from high resolutions. If you edit graphics in Corel-DRAW!, Micrografx Works, or some other application (and use a small monitor), you should choose a card that lets you switch resolutions, so you don't have to strain your eyes when editing text. Whether you use a 14- or a 21-inch monitor, editing graphics in 640 x 480 mode is hardly adequate. You'll get a much better WYSIWYG representation of what the final output will look like at 1024 x 768. Desktop publishers also benefit from the higher-resolution displays with large monitors, The idea is that the better your display, the easier it is to proof layouts onscreen, rather than by printing drafts. This saves both time and paper. Presentations and multimedia applications also benefit from high resolutions.

Millions of Colors

Perhaps even more confusing than resolution is color. Graphics cards are rated by the number of distinct colors they can display on a screen at one time. The range is from 16 colors to 16.7 million colors, with 256 being the most common number of colors. The number of colors a card is capable of producing depends on its bits-per-pixel rate. A rate of four bits per pixel, for example, provides 16 colors; a rate of 24 bits per pixel provides 16.7 million colors.

The 16-color model is the easiest one to use to demonstrate this concept. Since there are four bits per pixel, you have 4 x 4 (16) possible RGB combinations. As the number of bits per pixel increases, the possible combinations also increase substantially.

For most applications, 256 colors are fine. if you work with graphics, you should use high color. Most people, except for users of high-end photograph-editing software, such as PhotoShop or PhotoStyler, don't need 24-bit color.

(Note that just because a display is capable of only 16 or 256 colors, this doesn't mean that unsupported colors do not display. In Windows, for example, when an image calls for more colors than the graphics card is capable of, the additional colors are displayed through a process called dithering. Dithering mixes two or more solid colors to form another, If you have a low-resolution display that doesn't support many colors, you've probably noticed that some hues seem coarse. This is the result of dithering. in many applications, dithering is not a problem, but in graphics and photograph processing, where color purity is critical, it is not acceptable.)

Finally, as in everything else in life, there are trade-offs for these beautiful, high-resolution displays. The more colors and the higher the resolution, the more computing that is required of your CPU, which slows down your system. You can get around the demand that high resolution and numerous colors place on your computer by choosing an accelerated graphics card. Today's graphics cards come in four color standards, as depicted in the following table. Bits/ Mode Colors Pixel Name 4 minimum color 16 8 pseudo color 256 16 high color 32,768 24 true color 16.7 million

Caution: Just because a display adapter claims 32,768 or 16.7 million colors doesn't mean it supports them at all resolutions. When you increase the number of colors, the display adapter needs more memory to store the additional information. When looking at a card's color (and resolution) specifications, make sure it's capable of the number of colors you need at the desired resolution. Sometimes you can add RAM to a graphics card to increase resolution and color capabilities. You should also be careful that the card is shipped with a Windows driver (software that lets Windows use the card) that supports the number of colors and resolutions you need. If you don't use Windows, make sure you have the needed drivers for the applications you do use.

Refresh Rate

If you spend a lot of time at your computer, be on the lookout for a card with a high refresh rate. Your eyes will be forever grateful. The refresh rate is the speed at which the screen gets repainted. If the refresh rate is too low, your monitor flickers, which is annoying and hard on the eyes. it can cause headaches and lead to long-term vision problems.

Refresh rates are measured in hertz (Hz). A rate of 72 Hz means the screen is refreshed 72 times per second. Anything less than 72 Hz can cause noticeable flicker. Just because a card claims "up to 72 Hz" doesn't mean it supports that rate in all modes, Match the refresh rate to the number of colors and resolution at which you plan to use the card.

Interlaced Versus


Also critical to how a display system treats your eyes is whether or not it's noninterlaced. In an interlaced display, the electron gun paints every other line on the monitor each time it is refreshed - first, even lines and then odd lines on the next trip down the screen - which causes flicker. Many graphics adapters claim to be noninterlaced, but if you look closely at the advertising material or documentation, you'll see that they are interlaced at higher resolutions. Remember that the monitor must also support noninterlacing in the modes you plan to run.


Once the display adapter collects a screenful of data from the CPU, the video signal moves on to the monitor. The monitor uses an electron gun to paint the picture. The electron gun, which scans back and forth very rapidly, causes phosphors on the inside of the screen to glow. On a color monitor, the phosphors are red, green, and blue (RGB). Depending on the color capabilities of the graphics card, RGB combinations are mixed to create other colors - up to 16.7 million, which, by the way, is far more than the human eye can discern at one time.

The phosphors glow for only a small fraction of a second, so the electron gun must repaint refresh) them many times per second. The electron gun paints the screen one line at a time. When it finishes one line, it moves down to the next. When it reaches the bottom of the screen, it moves back to the top. The rate at which the electron gun repaints the lines is the refresh rate. The rate that the gun moves from the top to the bottom is the scan rate. As mentioned, the two primary considerations when buying a monitor are its size and whether it supports the resolution and refresh rate of the graphics card in your system. Some other things to consider when purchasing a monitor include multiscanning, dot pitch, and screen type.

Before looking at monitor-specific concerns, however, let's briefly review the issues that affect both monitors and graphics cards.

Resolution. Remember that the monitor must support the resolutions of the graphics card, including the highest one you plan to use. The good news is that you don't have to worry about buying a monitor that supports the number of colors you need. All color monitors support as many colors as your display adapter can generate.

Refresh rate. The monitor also must have the same refresh rate as your graphics card at the resolutions you plan to use. Again, make sure the desired resolutions and desired refresh rates match. Just because a monitor supports 72 Hz at 640 x 480 doesn't mean it will at 1024 x 768.

Screen size. Remember that it's important to match screen size to text size. However, where the size of your monitor really counts is in graphics and page layout applications. (Large monitors also help immensely when giving onscreen presentations to sizable audiences.) When laying out a double-sided, two-page document, for example, the extra screen real estate provided by a large monitor is very helpful. A 19- to 21-inch screen provides a much more accurate WYSIWYG view of the final document. This makes it easier to judge how well elements line up and to assess your overall layout, and it saves a lot of time by reducing the number of printed drafts needed.

Having reviewed the primary considerations, we can turn to monitorspecific concerns.

Multiscanning. Multiscanning refers to the monitor's ability to synchronize refresh rates automatically. Basically, this allows you to use different graphics cards with the same monitor. It also allows you to switch in and out of DOS applications from Windows without having to manually adjust the monitor.

Dot pitch. The size of a monitor's pixels is measured by dot pitch. The smaller the dot pitch, the crisper and cleaner the display. A good rule to follow is that 16-inch or smaller monitors should have a dot pitch of 0.28 mm or lower; 17-inch or larger monitors can get by with 0.31 mm or lower.

Screen type. The screen type can also affect the quality of your display. All monitors should contain an antiglare mechanism, either a separate coating on the screen or a built-in filtering device. Some people prefer flat screens to the traditional convex (or spherical) designs. The theory is that the flat screens more closely represent a sheet of paper.

Before You Buy

There are, of course, some other things to think about when upgrading your display system. Chief among these other considerations is price. Monitors and graphics cards are designed for a variety of applications, ranging from simple word processing to very highend graphic design. Naturally, the demands of digital photograph editing are much higher than, say, balancing your checkbook in Quicken.

Prices for graphics cards and monitors run from reasonable to absurd. You can pick up a good Super VGA graphics card for between $150 and $500. Or you can go to the extreme and choose a high-end graphics design station card for upwards of $3,000. When looking at the vast selection, it's difficult to tell why some cost so much more than others. The differences in quality and speed are often indiscernible. Monitor prices also fluctuate dramatically. However, since monitor prices generally vary directly with size, refresh rate, and resolution, and inversely with dot pitch, the pricing seems to make a lot more sense than the pricing of graphics cards.

When you start doing your research, you'll find that there are hundreds of cards and monitors available. (That's the reason I didn't mention any by name in this article. There are so many good ones that I didn't want to penalize vendors by not mentioning them.) The best test for a graphics display is to see it in action. If you can, get a demonstration. Ask to see the applications you run displayed, and put them through their paces on a system with your prospective adapter and monitor installed. If you buy through mail order, make sure you get a money-back guarantee.

Running Windows at the Speed of Light

A common complaint among users who switch from DOS characterbased applications to Windows is that Windows' GUI (Graphical User Interface) slows down their computers. Depending on the machine in question, the performance hit can be substantial.

The reason for the sluggishness is that, unlike character-based applications, the Windows interface uses every pixel on your monitor to paint the screen. This requires hundreds of times more information flowing from the CPU to the screen than the average DOS application.

This rush of information causes an immense logjam at the bus port, where the display information is passed on to the graphics card. One way to relieve the bottleneck is with a graphics acceterator. These cards take the bulk of the display processing on themselves, which frees up the CPU to do more fundamental tasks, such as calculating your spreadsheet or sorting a mailing list.

A number of accelerator cards are available, ranging widely in price. The cost of the accelerator depends primarily on supported resolution, number of colors, and refresh rate. The cards also come in many configurations, with various coprocessor chips and RAM configurations.

While I am not usually reluctant to recommend one product over another, the field here is wide open. The important issue in this category is not what chips are on the board, but rather the board's performance. How fast does the card speed up screen redraw in Windows? Some claim up to 30-fold speed boosts, but double, triple, or quadruple the speed of your current display system is more likely, especially if you work with large graphics.

It takes a lot of horsepower to display thousands of colors at high resolution. Most Windows users should look into accelerated graphics cards. The immense increase in performance far outweighs the small increase in price. In some cases, you'll pay only $50 to $100 more for an accelerated version of a vendor's graphics card.

In other words, the only reason not to go for an accelerated card is if you believe you'll never need to display more than, say, 256 colors at 800 x 600 resolution.

Catching the Local Bus

Another way to speed up Windows is with a local-bus graphics card. However, the only way to get one is by buying a new computer-one equipped with a local-bus port on the motherboard.

Most computers interface with graphics cards at 8 or 16 bits. However, today's 386 and 486 machines process data at 32 bits. The result is a bottleneck between the computer and the display adapter. The local bus is a 32-bit bus port that holds a 32-bit adapter, which doubles the rate at which the computer can send data to the monitor.

If you're in the market for a new computer to run Windows, especially Windows graphics applications, such as CorelDRAW! or PhotoFinish, make sure your new machine is equipped with a local-bus display system.

Which is more important? An accelerated ISA-bus card will actually drive your display faster than an unaccelerated local-bus card.

Movies on Your Monitor

The word video brings to mind renting Terminator 2 at the video store or watching Madonna on MTV. Recent hardware and software technology has brought motion pictures, or video, to the computer screen. As with the desktop publishing craze of a few years ago, it won't be long before virtually anybody can create and edit videos on a computer.

Personal computers, both Macintoshes and PCs running Windows, process video with one of two standards: analog or digital video.

Analog Video

Analog video is the standard used by TVs, VCRs, laser disc players, and camcorders. Analog video is typically stored on videotape or videodisc.

To use analog video with your computer, you'll need a special display adapter known as a video-in-a-window card, You can then run video from any VCR, TV cable, or other analog device. One of the more popular video cards is Creative Labs' Video Blaster,

Digital Video

Digital video is a digital form of video that can be stored as a computer file. Two examples are Microsoft's Video for Windows and Apple's QuickTime, These full-motion video standards run with or without a video board; however, for the best performance, you need the additional hardware.

If you're looking for a quick, inexpensive, and easy way to put video in Windows, choose Video for Windows. It's easy to install and comes with several video strips to get you started.