Classic Computer Magazine Archive COMPUTE! ISSUE 156 / SEPTEMBER 1993 / PAGE S2

How to upgrade your 386 or 486 processor chip. (microcomputer processor chip) (Compute's Getting Stated With: Upgrading Your Processor)
by Richard O. Mann

One way to pull your increasingly old-fashioned computer back into the forefront of technology is to upgrade its central processing unit (CPU) by swapping out your existing 386 or slow 486 chip for a hot, new 486 screamer. (Pentium chip upgrades are still in the future.)

However, not.all computers are candidates for a chip swap. Many popular mid-tier brand companies-such as Leading Edge, Packard Bell, Hyundai, and Epson-built their machines in a non-standard way, making upgrading impossible except perhaps with their own proprietary equipment. If you bought a more generic clone, you will have an easier time upgrading your CPU.

Who Can Upgrade?

You can upgrade even an old 286 chip to a 486, but it won't help much because the bus and the rest of the computer's components will slow everything down. A full motherboard upgrade is often the better choice for a 286, because it replaces many of the bottle-necked components.

Before beginning any upgrade project, consider the computer's age. Older computers may be like my first car, a four-year-old Mercury that was in pretty good shape. After a year, things began to fail. First, I had to replace the starter solenoid. Then came radiator problems, a ring job, alternator replacement, and so forth. After a couple years, I'd replaced almost everything under the hood. When the starter solenoid went out again, I knew it was time to get rid of the car. if your computer is aging, replacing the CPU may not be cost effective if the other components are due to wear out soon.

Any 386SX or 386 computer that's built to industry standards is a likely upgrade candidate. Finding out if it can be upgraded can be a ticklish task, though, because the upgrade vendor can't be expected to know the exact configuration of all of the thousands of clones built over the years. You'll need to consult with the upgrade vendor and perhaps the computer manufacturer to get all the information needed to determine if an upgrade will work. Some older units may require a BIOS upgrade along with the chip swap.

If you have a 486SX or 486DX that runs at 16,25, or 33 MHz, you're in luck. They're virtually all upgradable through intel's Over-Drive technology. Many have a separate socket built into the motherboard just for the purpose of inserting a clock-doubling 486 chip. it replaces the original CPU by completely disabling it and taking over its functions. In computers without the extra socket, you simply replace the original CPU chip.

What's the Benefit?

If you upgrade your 33 MHz 486DX by putting in an OverDrive chip, you will increase the speed from 33 MHz to 66 MHz. That's twice as fast-or is it?

Yes, some functions will be exactly twice as fast. Other functions, however, won't change at all. The exact amount of performance gain for any given task will vary, depending on which of your computer's resources are used to accomplish the task.

Changing a 33 to an overdriven 66 doubles the speed of functions with in the CPU, but the system continues to communicate with all the other components at the original 33-MHz speed. Thus CPU-intensive tasks such as calculation, record sorting, and word searches take place at twice the speed. But when the task involves getting data from the disk, rewriting the screen, or other non-cpu functions, there's liftle difference. Since almost all tasks involve both kinds of operations, the overall speed increase will be less than double, but still quite noticeable.

Replacing a 486SX with a 486DX Overdrive chip adds a math coprocessor to the system. This speeds up floating-point math operations, which are calculation-intensive tasks such as the mathematical operations in spreadsheets and the vector graphics calculations in CAD programs.

Converting a 386 computer to a 486 gives additional speed over the mere clock speed because the 486 thinks faster. In this rarefied atmosphere, everything makes a speed difference. An Intel 486DX chip has an 8K internal cache, for instance. This cache buffers data that the CPU would normally obtain from the system's RAM memory. If the CPU can read and write data through the cache rather than the external RAM, it's faster. Yes, even the speed difference between the CPU and external RAM is significant. In a clock-doubled system, the internal cache operation becomes even more significant.

A 486DX chip includes a built-in math coprocessor, but a 486SX doesn't. (Actually, it does, but it's masked off and doesn't function. Intel took a lot of heat for intentionally disabling part of the CPU chip, then selling it for less.) Thus, the speed difference between a 386DX and a 486SX of the same clock speed will not be overwhelming. There are, however, other efficiencies in the internal operation of the 486 chip that make it dramatically faster than a comparable 386 chip.