On June 4, 1995, AMD released its DX4 CPU, about six months after Intel released its DX4 CPUs. The AMD CPUs weren’t quite as fast as Intel’s DX4s, but they proved very popular because of their value for money. While I didn’t see AMD’s DX4 in many name-brand PCs, smaller manufacturers, especially local clone shops, sold them extensively. In the June 5, 1995 issue of Infoworld, an unnamed AMD spokesperson said they expected to sell 12 million 486-class chips by the end of 1995.
What a DX4 CPU was
In spite of the name, DX4 CPUs were clock-tripled, not quadrupled. Intel said the “4” in DX4 referred to the “4” in 486. AMD and Cyrix followed Intel’s naming conventions.
AMD’s DX4 came in four speeds: 75 MHz, 90 MHz, 100 MHz, and 120 MHz. Intel only offered 75 and 100 MHz. There wasn’t much point to the AMD 90 MHz part because it used an odd 30 MHz bus speed. It made more sense to just go with the 100 MHz part if you were chasing value, or the 120 MHz part if you wanted higher performance.
Intel priced its DX4 chip high. It was almost as if since it was almost as fast as a Pentium, Intel priced it like a Pentium. But the shops near me charged the same price for an AMD DX4-100 as they did for an Intel DX2-66. So unless you were really set on buying Intel, it made sense to get the AMD. The AMD DX4 was slower than the Intel DX4 because it had 8K of L1 cache like a DX2, where Intel gave its DX4 16K of L1 cache. But the AMD DX4 was faster than a DX2, only slightly slower than an Intel DX4 but the same price as a DX2. So buying AMD felt like getting 33% more performance for free.
How AMD’s enhanced DX4 closed the gap with the Intel DX4
AMD later released an enhanced version of its DX4 that offered writeback cache and increased the size to 16K. But it cost more. In ads from early 1996, I found the enhanced DX4-120 selling for $99, versus $67 for the regular version. I never thought the writeback mode and 8K more cache was worth the premium. It was faster and performed more like an Intel DX4. But it wasn’t 50 percent faster than the vanilla AMD DX4.
My mindset when building systems at the time was that inexpensive Pentium clones would be available within 24 months, so it was wiser to put the $32 toward a motherboard with PCI and a PCI video card that you’d be able to use with a Pentium motherboard rather than getting the fastest possible 486-class CPU and then having to replace it and a VLB video card when you upgraded. I reasoned you’d save more in the long run that way.
Why people bought AMD 486DX4 CPUs
The vanilla AMD DX4s were an outstanding value in their time. In the back pages of PC Magazine, I found DX4-120 motherboard/CPU combos selling for $160 advertised next to an Intel Pentium 75 CPU for $168. The motherboard for the Pentium cost $159. So an AMD DX4-120 motherboard and CPU cost half as much as a 75 MHz Pentium while only running 10-15 percent slower. It was an affordable choice that was fast enough to run Windows 95 and most games on the market at the time.
I built AMD DX4-based PCs for several friends in the 1995-96 timeframe.
The caveat with the AMD DX4 was that it ran on 3.3 volts rather than the 5 volts of an Intel 486 or DX2. Today you can use a Socket Blaster or similar project to run an AMD DX4 in a motherboard that expects a 5-volt CPU. Such adapters existed in the 1990s but they weren’t easy to find. Running at 3.3 volts helped the chip run cooler, but AMD couldn’t run its faster 486s at 5 volts anyway. This was a concession Intel won in court when it tried to keep the AMD 486s off the market. Intel didn’t want AMD selling 486s at all, but limiting them to 3.3 volts helped preserve the market for Intel’s high-margin Overdrive upgrade CPUs.
AMD was working on a Pentium-class CPU, the K5, to compete with Intel, but the K5 was late. Intel was under no pressure to keep pushing the 486, but AMD had to keep pushing the 486 to higher clock speeds to continue to have something resembling a mid-market CPU. AMD’s 5×86 CPU, announced about three months later, was just a 486 running at 133 MHz, using a 33 MHz bus and a 4x multiplier.
David Farquhar is a computer security professional, entrepreneur, and author. He has written professionally about computers since 1991, so he was writing about retro computers when they were still new. He has been working in IT professionally since 1994 and has specialized in vulnerability management since 2013. He holds Security+ and CISSP certifications. Today he blogs five times a week, mostly about retro computers and retro gaming covering the time period from 1975 to 2000.
did 3.3 volts run cooler and less energy than the 5-volt CPU?