What upgrade kits are available? (microcomputer upgrade kits) (Compute's Getting Stated With: Upgrading Your Processor)
by Richard O. Mann
If the miasma of numbers and letters in the chip names is giving you a headache, perhaps a few words of explanation can help clear things up.
Intel Corporation designs the original PC chips - from the first 8088 processor in the original IBM PC to the latest CPU chip, the Pentium (which would have been the 586 had Intel not felt a need to abandon its number-naming scheme). After each new generation of chips is released, other chip manufacturers clone them by creating as compatible a chip as they can. Advanced Micro Devices (AMD) has been at it the longest; Cyrix joined the competition in recent years. As we go through the mug book of current chips, you'll see both AMD and Cyrix chips, along with the Intel chips.
Starting from the chips you'll be swapping out, here's the lineup of today's chip market.
Intel 386SX. Available in speeds from 16 MHz to 33 MHz, this workhorse chip uses a 32-bit bus internally and a 16-bit bus externally while offering full 386 multi-tasking capabilities. It has the equivalent of 275,000 transistors.
Intel 386DX. The DX model is the full 386 chip, running at 16 MHz to 33 MHz and using a 32-bit bus both internally and externally. It also has the equivalent of 275,000 transistors.
Intel 386SL. Available in 20 and 25 MHz speeds, the 386SL is similar to a 386SX in that it uses a 32-bit internal bus and a 16-bit external bus. It was designed for use in laptop computers, because it has both cache and memory controllers on board and uses less power. Created after the 486 chip for this special use, it has 855,000 transistors.
Am386DX. This is the monopoly-busting 386DX chip from AMD; it runs at speeds of 25, 33, and the unique 40 MH. It uses a 32-bit bus both internally and externally and accomplishes this with only 161,000 transistors. Its lower price at introduction forced Intel to drop its prices.
Am386SX. AMD's popular 386SX is like the Am386DX except for its 16-bit external bus. Several power-saving features were built-in, so it consumes 35 percent less power than Intel's 386SX.
Intel 486SX. Available in 16 to 33 MHz models, this 900,000-transistor chip is a 486DX with the math coprocessor masked off. It uses a 32-bit bus both internally and externally and has an 8K internal cache. Its enhanced microcode also contributes to its speed.
Intel 486DX. Running at 25, 33, and 50 MHz, the 486DX uses 1,200,000 transistors, a built-in math coprocessor, an 8K cache, and enhanced microcode to perform its high-speed magic. It uses a 32-bit bus internally and externally. (Trivia: The 486DX is 50 times faster than the 8088 chip in the original IBM PC.)
Intel 486DX2 or OverDrive Chip. The DX2 doubles the internal clock speed of a 25-MHz 486DX to a speedy 50 MHz, or doubles a 33-MHz 486DX to an even speedier 66 MHz. The speed increase is only within the CPU; the external bus runs at the original clock speed. When sold to be used in a new computer, it's called a DX2. When sold as an upgrade to a current system, it's an OverDrive chip.
Cx486SLC. This 20, 25, or 33 MHz chip from Cyrix uses an internal 32-bit bus and a 16-bit external bus. With only 600,000 transistors, a 1K cache, and no math coprocessor, it's different from an Intel 486SX or DX. Intel argues that it's really performs more like a 386 than a 486.
Cx486DLC. This one is Cyrix's true 486-compatible chip, with a 32-bit data path internally and externally, a 1K cache, a built-in math coprocessor, and 600,000 transistors.
Cx486DRu.sup.2. Cyrix's name-convention-busting Cx486DRu.sup.2 chip is Cyrix's answer to Intel's Dx2/OverDrive chip. It's a 600,000 transistor clock-doubler designed as a replacement unit. (DRu stands from Direct Replacement upgrade.) It's available to double the speeds of 16, 20, and 25 MHz machines. Its bus, of course, is 32 bits internally and externally. it's a little taller than an Intel 386DX chip, so it may not fit into computers with limited headroom over the chip socket.
Pentium. See the companion article, "Future Upgrade Options," for the details of this latest Intel processing miracle.