How a monitor works

by Alan Stark.
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Monitors have evolved from simple monochrome displays to today’s high-resolution Super VGA. Monitors vary in price because they also vary in quality. A monitor, no matter what its size, is only capable of producing so many colors and resolutions.

How a monitor works

How do all those colors get to the monitor? The back of the monitor’s screen, which is called a cathode ray tube (CRT), is coated with phosphors. Aimed at the CRT is an electron gun. As the video card sends a signal to the electron gun, the gun shoots electrons at the CRT, causing the phosphors on the CRT to glow.

The gun fires constantly at the CRT from left to right and from top to bottom. The glow of three phosphors, red, green and blue, creates 1 pixel. The combinations of lit pixels create a pattern recognizable to the human eye, and the speed at which the images on the screen change presents the illusion of movement and a flow of colors onscreen.

At some point, you may have run across a monitor’s refresh rate, whether you read the monitor’s manual or saw it on the monitor’s specifications label. A monitor’s refresh rate refers to how often the electron gun is capable of redrawing the screen. Another term often included with the refresh rate is dot pitch. A monitor’s dot pitch is simply the distance (in millimeters) between two dots of the same color on a monitor. For example, an average monitor would have a dot pitch of .28 millimeters. An above average monitor may offer dot pitch as tight as .24 mm.

Monochrome video

The first monitor type for PCs was a monochrome. As its name implies, with monochrome you got one color (well two if you count the black screen behind the colored text). Early monochrome monitors could display only text—no graphics— at a simple resolution of 720 × 350, which was fine for characters. The Hercules Graphics card followed suit (1982) with the same resolution, but offered the ability to display graphics. Graphics could be displayed as the card used a library of characters for text mode and a more intense mode for drawing graphics. To the user, the switch between these two modes was invisible.

Color video

Most models of monitors available today are at least VGA. VGA (which stands for video graphics adapter) allows the monitor to send an analog signal to X that controls the flow and depth of colors more superbly than pre-VGA models allowed. Super VGA-capable monitors allow monitors to display higher resolutions and richer colors. The amount of RAM on the video card determines the number of colors the monitor can display. Some monitors and video cards promise True Color, which allows for up to 16 million colors.

IBM introduced its first color monitors (1981) with the Color Graphics Adapter (CGA), which had the ability to use four colors at a pathetic resolution of only 320 × 200. The card could be switched to two colors, which would result in a slightly higher resolution.

In 1985, IBM introduced the Enhanced Graphics Adapter (EGA) that could display 16 colors at a resolution of 320 × 200 or 640 × 350.

IBM later introduced (1987) an adapter capable of even higher resolution with its Video Graphics Adapter (VGA). The original VGA card had 256K of memory and the ability to display 16 colors at 640 × 480 or 256 colors at 320 @ts 200. As you can see, the higher the amount of colors used results in a lower resolution. This card is the bare minimum for today’s monitors and video cards. VGA uses analog and allows users to select from over 260,000 shades of colors.

Video Electronics Standard Association

As you can tell from reading the preceding sections, IBM was, for the most part, in control of the standards for color video adapters and monitors. The Video Electronics Standard Association (VESA) is a collection of manufacturers that later set out to improve on IBM’s video technologies. The result was the Super VGA video card. While it’s not the most creatively named card, it is, well, super (at least in comparison to its predecessor VGA). SVGA can support:

  • 256 colors at a resolution of 800 × 600
  • 16 colors at 1,024 × 768
  • 65,536 colors at 640 × 480
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