Q. What is the difference between 16-bit, PCI and AGP video?

A. How many of you recall the days of IBM "AT" computers? (That would be the mid-'80s, and believe it or not, AT stood for "advanced technology.") In these machines, a 16-bit bus, or internal data-moving system, was the standard way for the video card to handle the images presented to it. That worked fine for years. But when the megahertz speed of the machines' microprocessors started to approach three figures, computer makers looked for ways to make the image on the screen better and better as well.

One bottleneck in putting screen elements, or pixels, on the monitor was the motherboard, the computer's main circuit board. Designers altered it and the video card slot to make them faster. The result was PCI (peripheral component interconnect) and AGP (advanced graphics port).

PCI allowed the motherboard to move data 32 bits at a time. This yielded a transfer rate between the computer and the screen of 133 megabits per second. Generally, the faster the transfer rate, the better the image.

AGP was an even faster way to get those pixels poppin' on the monitor. The initial version hit the market in mid-1997 with speeds up to 266 megabits per second. AGP does require that the computer's chip set specifically supports it, and you need Windows 95 OSR 2.1, Windows 98 or Windows NT 4.0 or later versions.

Purists will argue that video is a multidimensional issue and speed is only one aspect of what makes a sharper image. But why argue it? AGP is inexpensive enough to be on most new machines these days.

When I turn on my computer, I get "DMI error." What's that?

DMI stands for "desktop management interface" and is a relatively newfangled way aimed at making a personal computer on a network easier for the people in the systems office to manage.

The past few years have seen more and more reports from consultants about the TCO, or "total cost of ownership" of a PC. They have concluded that having a personal computer on a network is a very expensive proposition, what with all the maintenance they always seem to need. One way companies try to lower that cost is by altering the BIOS (basic input-output system) of the computer to put in DMI capability that allows the system administrator to see what is going on with a specific machine. Needless to say, this "solution" makes a whole new level of conflicts possible. Our reader has just come across one.

To fix a DMI error, you have a hodgepodge of places to start looking. For instance, if you have recently added a video card you got at a yard sale, it may not be compatible with the DMI-altered BIOS. Solution: Get a new card, you tightwad.

Some people who try to make their machines run faster than they were designed to go (this is commonly called overclocking) get this error message. Solution: Don't overclock.

Finally, there are reports that upgrading operating systems can cause conflicts between the new operating system and the DMI setting in the BIOS. Solution: Go to www.microsoft.com for updates and remedies.

I am having a problem upgrading my video card. The new card seems to install fine, but my monitor settings still indicate the old one.

Over the past five years, I have used gallons of ink telling readers to install the correct software "driver" for a new device. I should also have been saying that when you do so, make sure you get rid of the old stuff too.

So when you've installed a new device, go to the control panel and "add/remove programs" and remove any mention of the device you are replacing. If you are on top of things, you may already be using a program such as Uninstaller that will do this job better than the built-in utilities in Windows.

John Gilroy of Item Inc. is heard on WAMU-FM radio's "The Computer Guys" at 1 p.m. on the first Tuesday of the month. Send your questions to him in care of The Washington Post, 1150 15th St. NW, Washington, D.C. 20071-5302 or via e-mail at jgilroy@iteminc.com.