Video adapter function and location |
How does it work? | Judging a video adapter

A good video adapter can speed up your entire system and give your computer the flexibility to handle text, photographs, illustrations and even movies.

An up-to-date video adapter can bring new life to a tired old computer, and special-purpose video boards can turn your new computer into a true multimedia machine, capturing signals from TV sets or VCRs and producing professional-quality video output.

What's a video adapter and where is it?

Your video adapter is a circuit card inside your computer. The only part you can see is the port on the back of your machine that accepts the cable from your monitor.

In some systems, the video adapter is a card that fits into an expansion slot on the computer's motherboard. On many newer computers, the video circuitry is built right into the motherboard, and there is no separate video card.

The advantage of a separate video adapter is that you can replace it or upgrade it easily. Built-in video circuitry is usually less expensive to produce; it's one of the reasons that new computers offer so much horsepower for so little money. However, built-in video circuitry can be far more expensive to replace if it should fail or become outdated.

What does a video adapter do?

Your video board takes commands from your computer's CPU/microprocessor and produces signals that drive your monitor's electron gun. Inside the monitor, the electron beam strikes tiny clusters of red, blue and green phosphors on the inside of the screen. Those phosphors light up to produce colored dots, or pixels. Your eye sees those patterns of dots as images -- the first page of your novel, a scanned photo of your family or a dungeon from the video game Doom.

What makes a good video adapter? Basically, it's the ability to move lots of pixels with many colors at high speed. To accomplish this, modern boards incorporate video co-processors, or accelerators, which take the video work away from your computer's main processor. Instead of figuring out where to put each dot on the screen, your processor passes the work along to the video board, which frees up the main processor to do other things. Good video boards contain a substantial amount of memory to store screen images. More memory enables a video board to produce higher-resolution images with more colors. Video boards may also have special circuitry for handling 3-D drawings and video that conforms to an industry standard called MPEG.

Judging a video adapter

Although you'll hear a lot of "tweakspeak" when people talk about video adapters, two factors ultimately determine what you see on the screen: resolution and color depth. Most video adapters let you choose how much you want of each. The higher the resolution and color depth, the better the picture. Unfortunately, as image quality goes up, speed usually goes down. The best boards will provide the highest quality image with the fewest compromises in performance.

Resolution. This is the number of horizontal and vertical pixels the video board produces, expressed in terms of counts. For example, at 640 x 480 pixel resolution, your screen is divided into 640 dots across and 480 dots down. Why aren't the two numbers the same? Because your screen is wider than it is tall -- by a 4-3 ratio. Almost all video boards stick with resolutions close to this ratio.

The more individual pixels your video adapter can address, the more information you can view on the screen. That makes it easier to work with multiple windows, or you can display more spreadsheet cells at one time, for instance. Generally speaking, a better video board will offer higher maximum resolution than a less-expensive board.

However, don't fall into the resolution trap. Higher resolution isn't always better. That's because most graphical operating systems, including Microsoft Windows and the Macintosh OS, define images and fonts in terms of pixels. For example, this letter "A" may be 10 pixels high and 12 pixels wide. At higher resolutions, the "A" will be smaller because the pixels that create it are smaller. If the "A" is too small, you can't read it. So, if you're using a standard 14- or 15-inch monitor, super-high resolutions may be virtually unusable for anything but editing photographs.

To get around this problem, you can always buy a larger monitor. As a cheaper alternative, the software driver that comes with your video adapter may offer you the choice of using larger-than-normal fonts at higher resolutions.

That said, here are the standard resolutions you're likely to encounter:

• 640 x 480 pixels. This is the so-called VGA standard, named after the IBM Video Graphics Array. The VGA was the first IBM color video board to produce a "natural" 4-to-3 resolution. Most PCs are delivered with the video board set to 640 x 480 pixels, although many users quickly switch to higher resolutions.

•800 x 600 pixels. The beginning of the so-called Super VGA (SVGA) standard. Many users with 15-inch or larger monitors find that this resolution offers readable screen fonts and enough elbow room for multiple windows.

• 1,024 x 768. Desktop publishers and graphics professionals like this resolution because they can see an entire page on the screen. However, you'll need the eyes of a fighter pilot to read the standard screen fonts, unless you have a 17-inch or larger monitor.

• 1,280 x 1,024 and higher. These settings are for high-resolution graphics work only. Don't bother with these unless you have a 20-inch monitor.

Color depth. Your monitor can light up red, green and blue phosphors at various levels of intensity. As a result, it can produce an almost infinite variety of colors.

Your video board is more limited. It has to determine how many different levels of intensity it's willing to offer for each pixel. This requires not only speed (because it has to redraw the screen, typically, 60 to 72 times per second), but also a substantial amount of memory.

The original VGA adapters used only four bits of memory per pixel, which produced a maximum of 16 colors at 640 x 480 resolution. That made it virtually impossible to display natural-looking photographs without switching to a lower resolution.

Today's video adapters are capable of much greater color depth. In fact, most will offer you a variety of color levels, along with a choice of resolutions.

For normal use, a popular choice is 256 colors at 800 x 600 pixel resolution. That's enough resolution for decent detail, and enough colors to produce pleasant photographic images on the screen. However, it's not enough for graphics professionals who need to match what they see on the screen to the capabilities of color printing presses.

So-called "true color" video adapters can use 24 bits of information per pixel, which translates into 16.7 million possible colors. Some experts say that's the maximum number of colors the eye can perceive, although others say the true number is higher. In any case, if you have the horsepower for 24-bit video, your screen images will look terrific.

Video memory. Your video adapter stores in its own memory banks the information it needs to draw the screen. The amount of memory in your video adapter -- and the kind of memory it uses -- determines how fast the video adapter performs and how many colors it can produce at different resolutions.

Better video boards use expensive VRAM (Video Random Access Memory) chips. They are able to move images faster than regular memory chips can because your processor can read and write to them at the same time. Less-expensive boards use standard DRAM chips, but manufacturers have come up with a variety of tricks to boost their speed.

You'll need more memory to produce more colors at a higher resolution. The video systems on many new computers come equipped with two megabytes of video RAM, while a handful come with four megabytes. A few low-end systems offer only one megabyte -- avoid them. You can add more memory to most video cards if you like. Here's how much memory you'll need for 24-bit, true-color displays at different resolutions:

As a rule of thumb, unless you're doing serious graphics work at very high resolutions, a two-megabyte video card will suffice. But if you have a choice between similar computers with different amounts of Video RAM, choose the highest for best video performance.