Buy a 386XS and save a bundle. (microcomputers) (column)
by Mark Minasi

Buying a new PC or upgrading an old one? Want some good advice? Don't buy speed. For the past three years, big corporate buyers and the PC trade rags have been beating the drum about the great new PCs: 25- and 33-MHz 386 and 486 systems have become de rigueur. In fact, one large magazine recently said that 25-MHz 386s were the new entry level system.

Phooey on that, I say. Your best bet is to buy a 16- or 20-MHZ 386 or SX, save a pile of money over the "faster" models, and plow that money into faster video and disks. The result will be a faster and cheaper system than that 33-MHz pile driver you wish you could afford. Here's whY.

Your computer's speed is mainly determined by four things: the CPU's speed, its memory subsystem, its disk subsystem, and its video subsystem. Making just one of these parts super-fast is of no value, since the relative pokiness of the other parts holds back the whole system. in essence, the system is no faster than its slowest part.

Let's look first at the CPU. You definitely want a 386 or 386SX. There's little price difference over a 286, and the 386 family can do so much more than the 286. Don't worry about losing in the long run by buying an SX; software-wise, it works just like a full 386 (a full 386 is officially called a DX). You don't buy 386-family PCs for the speed; you buy for the capabilities, like Windows 386-enhanced mode.

What do megahertz cost? Comparing the prices of a few representative bare-bones motherboards, you'll find that a 16-MHz SX motherboard costs $325 and a 25-MHz DX motherboard costs 900. How do they compare when doing real work? My advice is to try it. You won't be able to tell the difference for most realworld applications. Why is a 16-MHz SX so similar in apparent speed to a 25-MHz DX? It has to do with the video and the disk. You see, the video is controlled by a video board, which plugs into the PC's bus. The disk is similarly controlled by the disk controller board, which also plugs into the PC's bus. And there's the rub.

Virtually all PC systems today run their buses at 8 MHz. Spend a zillion dollars on a 33-MHz DX, and it's really only the CPU that runs at 33 MHz. All the expansion boards run at a mere 8 MHz. Every time that 33MHz computer talks to the video board, the whole system slows down to 8 MHz-Utto for every disk access. Even worse, it probably doesn't run at a full 8 MHz, since the video or disk board may well be running slower than 8 MHz.

That's why it's silly to pour money into fast CPUs while hobbling them with slow peripherals. By spending less on the CPU and more on drives and video, you balance your system. Here's how.

First, get a fast disk. Disk speeds are called access time or seek time, and they are measured in milliseconds (ms), thousandths of seconds. With access time, the smaller, the better. There is no reason why you should get stuck with a disk with an access time slower than 28ms, yet I See clonemeisters still dumping 65ms drives on the public! Insist on 28ms or faster.

Get a fast disk controller. Disk controllers are rated by their interleave factor. Most 286 and 386 systems nowadays contain a 1:2 disk controller, a $90 item. For $20 more, you can purchase a 1: I disk controller. Such a controller can read the data off your disk at twice the speed of a 1:2. Why does anyone ship 1:2 systems, when 1: I costs only a bit more? Until recently, 1: 1 controllers were four times the price of 1:2 controllers. As a result, 1:2 controllers became a standard, and old habits die slowly, I guess.

Get a fast video board. Ensure that you have a 16-bit VGA board, rather than the slower 8-bit VGA board. Once, 8-bit boards were half the price of 16-bit boards, but no more. Good 16-bit VGA boards can be had for around $80.

Your PC's memory subsystem also affects both your PC's up-gradability and its speed. You've probably heard the terms memory cache, interleaved memory, and wait states. They all refer to methods of interfacing the CPU to its memory. There's not enough room here to explain all of them-memory would provide enough fodder for several articles. Basically, though, no one today makes inexpensive memory that is fast enough to keep up with today's CPU speeds of 16 MHZ and up. So manufacturers hook up fast CPUs with slow memory and build ticks into the system to minimize the effects of this mismatch. Wait states are the worst way to handle the speed mismatch, interleave is a much better way, and cache is the best of all. Cache, unfortunately, also costs more-perhaps too much. Don't settle for wait states, however; you want a no wait-state, interleaved-memory system.

So you see that buying the 33-MHz screamer with the 8-bit video, 1:2 interleave, and 48ms hard disk isn't such a good idea after all. I recently bought a 16-MHZ SX with 16-bit video, 1: I interleave, and a 120MB hard drive (28ms access time). Lots folks think it's a 25-MHz, an who am I to dispel their illusion?