By Marc Spiwak
Technical Editor

There's more than a grain of truth to the statement that PC hardware is obsolete the minute you take it out of the box. Video, like all other computer hardware, evolves so quickly that most users' wallets just can't keep up. You might own a relatively new computer, but find that its video setup is just not as fast as the video in an up-to-the-minute system. It's relatively easy to upgrade video performance on a recently purchased system, sometimes simply by adding more memory to the graphics adapter. But what if you're using a 486 or slower machine? Can these systems be upgraded? Will the upgrade be worthwhile? What do you need to make the upgrade? We've got the answers to these questions, plus details about the do's and don'ts of video upgrades.

Before you think about upgrading, you should understand how a graphics accelerator works.

In an unaccelerated system, graphics information is processed by the CPU. If a graphics card is installed in a PC, all display information is sent there. This makes for speedier processing and frees up the CPU for more important tasks. Information processed by the graphics accelerator chip is sent to the card's on-board memory. The better the card, the faster this transfer will occur. Information in the card's memory is then converted into a signal that is fed to the monitor. The monitor, in turn, uses this data to refresh its screen.

A graphics card's bandwidth determines how much information can be piped through it at once. The data bus between the CPU and the graphics card is always 32 bits wide.

A video card's "64-bit" or "128-bit" designation actually refers to the data pathway that shuttles information between the accelerator chip and the video memory. The wider the bus, the faster the card can send processed information to its own memory.

We ran benchmarks on a 486 DX2/66 system with an ATI Mach 32 card; these showed an average of 3.7Mpixels per second. Upgrading the video card to a Diamond Stealth 64 VLB yielded results that were 15 percent to 25 percent faster, depending on the test, and the speed improvement was noticeable.

If you own a Pentium PC with decent performance in everything but video-which can be the case with some older, entry-level Pentium systems-you might get some benefit from upgrading video. Then again, you might not, depending on the applications you are running. In the table, you can see that upgrading 64-bit video to 128-bit offers only marginal improvements in our Wintune video test scores, which reflect graphics tasks you might employ in the course of most business days. We tested one 64-bit card and two 128-bit cards, and all test results were consistent within the margin of error of our test.

The Wintune benchmark showed that a good 64-bit card will give results similar to those of a 128-bit card at resolutions to 1024x768, and color depths to true color. There are applications-such as MPEG video playback, which requires fast shifting of large amounts of pixel data-where the 128-bit card might really outpace its narrower cousin. We didn't test such applications for this article, however, concentrating instead on more mainstream business tests.

The amount of memory on a video card does not necessarily tell you how well it accelerates video. On-board memory is simply used to hold information. More memory is needed when you increase your screen resolution or the number of colors used.

Video cards come with different types of memory. The least expensive type, dynamic RAM (DRAM), is also the most common. Most mainstream cards have DRAM, which requires one clock cycle to bring information in and another to get it out. EDO RAM, or extended Data Out RAM, holds data active longer and offers better performance than DRAM in certain situations. VRAM, or video RAM, is both faster and more expensive than DRAM or EDO RAM. VRAM is so-called "dual-port" memory, which means it can simultaneously load and unload data on the same clock cycle.

You will soon see cards equipped with MDRAM, or multibank DRAM, which should equal or better the performance of VRAM. Other memory types will surface in the future.

The number of colors that can be displayed at once is directly related to the number of bits used to represent each pixel. Eight-bit color can display a maximum of 256 colors (28 = 256), while 16-bit, or high, color (216) equals 65,536 colors. True color, also known as 24-bit color (224), equals 16,777,216 hues.

Depending on the amount of memory on the card, you may have to make trade-offs between resolution and number of colors. A general rule of thumb: If you want a high-resolution display, you may have to settle for fewer colors, and vice versa. This, of course, depends on the amount of memory in your video card. A card with 2MB of video memory can display 65,000-plus colors at a resolution of 1024x768 pixels, while a 4MB card can display the full 16.8 million colors at the same resolution. A card with only 1MB of video memory is far more limited in what it can display.

It's not always the best idea to buy the most expensive card on the market-if you're not using graphics-intensive applications, why spend money for on-card memory you won't need? The average 640x480-pixel screen at 256 colors takes up about 350KB of memory. If this is your standard setup, a card with 1MB of video memory will suit you just fine. If you buy a graphics card with 8MB of VRAM, you're paying for power you don't need.

If you don't have to work with true-color graphics, you'll find 16-bit color more than adequate. For everyday work, 256 colors will do just fine. In fact, it's most efficient to work with 256 colors (video performance is best at this level) and change the settings only when necessary.

A 64-bit accelerator card with 2MB of memory is an excellent choice, even for most power users. A 64-bit on-board bus is necessary to distribute processed information effectively into the 2MB of memory, while a 128-bit card becomes more effective with 4MB of memory. Prices for 64-bit cards range from $200 to $400, while 128-bit cards start at $600.

The refresh rate of a video card describes how often the picture on the screen is redrawn. The less often a screen is redrawn, the more screen flicker you get. Some video cards will have a particular preset refresh rate for a given resolution, while others let you select the rate. A refresh rate of 70Hz or higher is easier on your eyes. Slower rates cause more flicker.

Now that you know the video card basics, you should be aware of some of the newer innovations.

One of the latest graphics add-ons is the 3-D accelerator card. These improve the quality of displayed textures and depths, making them more realistic. These cards are just starting to hit the scene, and are intended mainly for games and CAD. Prices range from $200 to $400.

Also new on the scene are cards that allow the playback of MPEG video. The better models have on-board hardware for MPEG playback, leaving your CPU free. An MPEG daughterboard will cost about $100.

New TV-tuner cards can be connected to a cable or antenna, allowing you to watch television on your PC. Many also let you capture video to your hard drive. TV tuners are available as add-on daughterboards and run about $100.

Soon you'll be able to feed cable TV signals into your PC, MPEG-encode them and record the works on a blank CD-and all with an entry-level machine. For now, you still have a multitude of video options. Let your needs--and your checkbook--be your guide.