Chipping Away At The Truth About Pentium Vs. 486

Q. My friend says that the 486DX2/66 and the Pentium 66 are the same speed. He says that it's like the Mercedes that goes 90 mph goes faster than the Volvo that goes 90 mph. He says the only reason that the Pentium goes faster is because of the PCI and the faster hard drive. I know that he is wrong. Please verify that he is wrong. Cameron Bruce

A. I'm not sure what your friend means about Mercedes doing a "faster" 90 mph than the Volvo, but you can consider yourself vindicated. The PCI bus and hard drives aren't the only things that make a Pentium 66 faster than a 486DX2/66.

Your friend is right that the bus - the data channel between the microprocessor and the rest of the computer - does make a significant difference. That 486DX2/66 is operating internally at 6 megahertz but communicates with the rest of the computer at only 33 MHz.

In contrast, the Pentium 66 runs at 66 MHz both internally and in communicating with the rest of the computer. That means faster overall performance.

But there are also other major differences between the Pentium and the 486 chips besides their buses that result in performance differences. For starters, the Pentium chip contains more than 3 million transistors, while the 486 chip has only about 1.2 million. The Pentium also employs a different, and more efficient, internal architecture than the 486 processor.

Q. I have a problem that I think relates to a Diamond Stealth Pro video card. My system works perfectly in Windows, but about 40 percent of the time when I go into a DOS window the system locks up, requiring a hard reboot. If it does go into the DOS window, the system works fine and will return to Windows fine. The problem appears to be random, and I've never detected a pattern of events that triggers it. I've unloaded all other drivers, but the problem persists, and I can't find any IRQ or DMA conflicts. The Diamond support line is always busy and they won't answer the faxes I've sent them. Do you have any ideas? Doug Brooks, Bellevue

A. Been there. When this sort of problem happens, you can figure the culprit is most likely either a corrupt or out-of-date video driver or a memory conflict. You can quickly check the video driver by switching to the standard VGA driver that comes with Windows and seeing if the problem goes away. If it does, contact the maker of the video card to make certain you've got the most recent driver and that it knows about the problem with the driver you have.

If you still have the problem after switching to the VGA driver, you should start looking for a memory conflict. Most likely your video card is using a segment of expanded memory that is occasionally being accessed by a DOS application, resulting in system crashes.

Try loading Windows by typing in the following command: WIN /D:VSX. This will load Windows in diagnostic mode which means, among other things, that it will not access expanded memory. If this solves your problem, you'll want to find what range of expanded memory your graphics adapter is using, then add the following line to the 386Enhanced section of your CONFIG.SYS file: EMMExclude=XXXX-XXXX. In place of the X's insert the range used by your video card. The easiest way to determine this range is to consult your graphics adapter manual or call the maker of the video card.

Alas, both courses of action mean that you're probably going to have to reach Diamond at some point.

Q. I've been reading articles that recommend using a 16550 UART chip with Windows because it can handle the added demands of a multitasking environment. MSD.EXE tells me that a 16450 UART is connected to my modem port (COM 2, US Robotics external 14,400 fax/modem). Nothing I read, however, tells me where to find this chip so that I can replace it. My guess is that it's soldered to a board somewhere so that means replacing a component board. Paul Garavaglia

A. First of all, the 16550 UART chip doesn't have anything to do with multitasking. It improves serial communications primarily by providing additional storage buffers to handle the faster flows of data between your modem and your computer.

Some systems, though not very many, come with a UART (universal asynchronous receiver/transmitter) on the motherboard. More often, the UART chip is located on an add-on I/O board that resides in one of your system's slots. Typically, the I/O board provides ports on the outside that you use for your mouse and/or parallel printer.

If you buy an internal modem, it will most likely include a UART 16550 chip on it, but since yours is an external modem it is almost certainly employing the UART chip on your I/O card. The simplest way to upgrade to a 16550 UART is to buy a new I/O card. You can find them at computer stores for under $50.

Q&A by Patrick Marshall appears Sundays in the Personal Technology section of The Seattle Times. Questions can be by e-mail at ptech@seatimes.com or 75300.2742@compuserve.com, or by postal mail at Q&A/Technology, The Seattle Times, P.O. Box 70, Seattle, WA 98111.