VGA, which stands for video graphics array, is currently the most popular standard for PC screen display equipment. Technically, a VGA is a type of video adapter (circuitry in the computer that controls the screen). IBM developed the VGA for its PS/2 line of computers (the name “Video Graphics Array” is an IBM trademark), but loads of other manufacturers make VGA add-in boards (that plug into a slot in the pc) and VGA chips (in some pcs, these VGA chips are built right into the main part of the computer, the motherboard). A VGA monitor is a monitor that works with a VGA adapter.

A standard VGA system displays up to 640x 480 pixels (little dots) on the screen, with up to 16 different colors at a time. In lower resolution, 320x 200 pixels, the screen can show up to 256 colors at once. These specifications are much better than the older video adapter standards, the CGA and EGA, but they’re not good enough for many people. If you’re buying a new system or replacing an older video adapter, make sure you get a “Super VGA” adapter, which can handle higher resolutions (800x 600 or higher) and many more colors. Remember though, that the higher the resolution and the more colors you have to work with, the slower the display will function, and the more memory you’ll need on the card.

Unlike EGA and CGA monitors, VGA monitors are analog devices, meaning they can display an infinite range of colors (the number of colors you see is limited by the VGA adapter, not the monitor).

When you’re shopping for a VGA monitor, keep several points in mind. First, if you want to use higher resolutions than the VGA standard of 640x 480, you need a multiscan monitor-a plain VGA monitor will not work at higher resolutions. Second, some VGA monitors give a sharper image than others. Partly, this depends on the dot Pitch: a monitor with a smaller dot-pitch (like .28mm) will have better image clarity than one with a larger dot-pitch (like .39mm).

A VGA monitor requires an interface card and a cable. You need to know how much memory is on the card. You may want to add more memory, especially if you plan to create and use complex graphic or photographic images. The VGA is the current standard right now in monitors, and as such is usually the most readily available.

Vector graphics are stored in the computer as a set of mathematical formulas describing the shapes that make up each image. When you display a vector graphic on the screen or print it, these formulas are converted into the patterns of dots you can see. Because the dots are not specified unit! you display or print the graphic, you can change the size of the image without any loss of quality, and the image will always appear at the highest resolution of whatever screen or printer you’re using. The term vector graphics means exactly the same thing as object-oriented (or just object) graphics.

The contrasting term is raster graphic (the terms raster and bitmapped are synonymous). In a raster graphic, the actual dots that make up the image you see are defined when the graphic is created, so the resolution is fixed; changing the size will make the image look coarse or muddy. See paint program for an example illustrating the fixed resolution.

Most Macintosh people use the terms object-oriented and bitmapped rather than vector and raster. Most PC people use both pairs of terms interchangeably.

Multiscan refers to a type of computer monitor that automatically matches the synchronizing signals sent from the computer’s video adapter (the video circuitry). On a standard television-type monitor, the image you see is formed by a single beam of electrons scanning lickety-split across the picture tube. The beam starts at one corner, traces a narrow horizontal line, then moves down a bit and traces the next line. The speed with which the beam travels horizontally and vertically (the horizontal and vertical “scan frequencies”), must match the synchronizing signals from the computer’s video circuits.

The problem is, the synch signals vary with each type of video adapter for PCs(EGAS, VGAS, Super VGA, and so on). Since the scan rate is fixed in an ordinary monitor, you can only use the monitor with one type of video adapter-a VGA monitor only works with a VGA adapter, and so on. By contrast, a multiscan monitor will work with many different types of adapters, within limits.

When you buy, be sure your monitor’s range of scan frequencies matches all the adapters you may use it with. At a minimum, it should have a 50-75 Hz (hertz, times per second) vertical frequency and a 30-50 kHz (kilohertz) horizontal frequency. The vertical frequency measures how fast the entire screen is “repainted,” and is also called the refresh rate. You should also insist on a variable frequency monitor, one that can match any frequency within those ranges, rather than one that simply operates at several different but fixed frequencies. And, by the way, multiscan monitors are more expensive than fixed-scan rate monitors.

There’s much less inconsistency in the Macintosh world, so a multiscan monitor isn’t so important. But many of them will work with a Mac

Monitor is another word for the computer screen. But “monitor” encompasses the whole piece of equipment, rather than just the screen part that you look at. You also might hear a monitor called a display, as in “Oooh, I got a new two-page display,” or VDT(video display terminal), as in newspaper journalism, or CRT (cathode ray tube), which is the technical term for a picture tube. However, flat panel screens like LCDS are not referred to as monitors, even if they’re housed externally from a computer.

Some monitors are built right into the computers, like in the small Macintoshes. When you purchase a larger Macintosh or most other kinds of computers, you must buy the monitor separate from the computer itself (that’s why they’re called “modular”). Monitor size is measured like a television, from one corner to the diagonally opposite corner.

Some monitors are monochrome, meaning they can show only one color on a background, like black on white (Macs), green on black, or amber on black (pcs). Grayscale monitors can display different shades of gray, rather than imitating the different shades with combinations of black and white dots. And there are many different color monitors. A color monitor can display any of several levels of resolution and can display varying numbers of colors, determined by several factors, such as amount of memory in the computer or the type of card that is controlling the monitor. See the section in Appendix A on how to read a computer monitor advertisement.

If an image is displayed on your screen or printed on the page in low-res (short for low resolution), that means you are seeing a low-grade quality. Some graphics are just low-resolution to begin with, such as graphics made in the paint file format at 72 dots per inch. Some graphics are created as complex, high-resolution images, but you may choose to display them on the screen or print them in low-res just to save time, since it takes longer for a screen or a printer to create the high- resolution version.

For instance, if you are producing a brochure on your computer and in the brochure you have several high-resolution photographs in full color, it can take a long time to turn pages or change views. So you can choose to view these images in low resolution while you are working, just so you can move around the screen faster. You can choose to print them in low resolution just so you get an idea of the look of the brochure without waiting to reproduce the entire high resolution images.

The lower the resolution, the less information there is in a given amount of space (in a square inch, for instance). It may mean that each pixel in that square inch of the screen is not providing enough information to resolve the image clearly, or it may mean there are less printed dots per inch on the page.

LED stands for light emitting diode. You know those little lights on your computer, usually near the hard disk, that flash while the computer is working? Those are LEDs. They work on the principle of electroluminescence, which refers to substances that glow when you apply electricity. LEDs were used in digital watches, but now all digital watches use LCDs because LCD stakes less power.

LEDs are ordinary diodes (the most basic electronic component) that, due to their composition, happen to glow red, green, or amber when energized by a couple of volts. They use less power than incandescent bulbs and last over 100,000 hours.

In a standard television-like computer monitor, an image is produced on the screen by a beam of electrons sweeping rapidly across the surface of the picture tube, lighting up the screen as it passes. Starting at the top, the beam traces one horizontal row across the screen, shifts down a bit and does another row, and so on, until the full height of the screen has been covered.

In an interlaced monitor, the electron beam takes two passes to form a complete image: it skips every other row on the first pass, and then goes back and fills in the missing rows. A non-interlaced monitor does the whole job in one pass, tracing each row consecutively. Interlaced monitors are easier to build and therefore cheaper, but as you can guess-they aren’t as good as non-interlaced monitors. The problem is that all things being equal, it takes twice as long to create the complete screen image on an interlaced monitor. That’s long enough to spoil the illusion that you’re looking at a steady picture, and the image on the screen flickers annoyingly. 

The dot pitch of a color monitor measures the size of the tiny individual dots of phosphorescent material that coat the back side of the picture tube’s face. The dot pitch helps determine how sharp the image looks, independent of the resolution (which is measured in pixels). A smaller dot pitch is better.

Here’s the technical scoop: Each point of light on a color monitor is formed from a triad of three separate dots of phosphor: one that glows red, one green, and one blue (the color you finally see depends on how intensely each dot in the triad is excited by the picture tube’s electronic beam). The dot pitch is the vertical distance between the centre of one dot and the next like-colored dot directly above or below it (the way the dots are arranged, pairs of like-colored dots are always two rows apart). The farther apart the centres of the dots are, the bigger the dots and the fuzzier the image. All other things being equal, a monitor with a smaller dot pitch is preferable to one with a larger dot pitch, though other factors are more important in determining image sharpness below a certain dot pitch threshold.

A dot pitch of .28 mm or smaller is ideal for 14- or 15-inch monitors; a dot pitch of .31mm or less for 17- to 20-inch monitors. Resolution, in pixels, is determined by the video circuitry in your computer. Depending on the resolution and on the dot pitch, a single pixel may occupy 4 to 16 separate phosphor triads.

CGA stands for color graphics adapter, the first IBM video card to permit graphics on the screen. We’re lucky they’ve come out with better models, because CGA graphics are gawdawful crude. With a CGA, your screen can show up to 640 dots across by 200 dots up and down, with only one color. Even at that maximum resolution, pictures look really blocky and out of proportion. Pictures will look even more blocky if you want 4 colors on the screen at once, since you’re then limited to 320 dots across and 200 down. If you can tolerate a totally chunky display of 160 by 200 dots, you can get a maximum of 16 colors on a CGA. Wow!

A CGA can display text too, but the characters are fuzzy looking and squished together, so they’re hard to read. And you may see an annoying sparkling effect called snow when you scroll the text. So don’t buy a computer with a CGA. And if someone gives you one, put in a VGA instead.

Many other companies besides IBM have produced video cards that work just like a CGA. Some pcs, including most laptops made prior to 1990, come with built-in CGA-Compatible circuitry. These variations are generically referred to as CGAs or CGA systems, trademarks notwithstanding. And since people don’t look at the video circuits too often, they generally end up using the term CGA to refer to their monitor, as in “I have a CGA screen.”