VIA Cyrix III and C3 CPUs

Last Updated on February 28, 2025 by Dave Farquhar

The VIA Cyrix III was a short-lived Socket 370 CPU produced by VIA using technology it acquired from Cyrix and Centaur, two makers of Socket 7 CPUs. VIA first introduced the Cyrix III on January 5, 2001.

When a Cyrix isn’t a Cyrix

Initially the Cyrix III used a 22-million transistor core designed by Cyrix, but that chip was never introduced because it ran hot and had lackluster performance. But VIA had two CPU design teams. Soon after acquiring Cyrix, VIA also acquired Centaur from chipmaker IDT.

Instead, VIA switched to a Centaur core with half the transistor count. Based on the Winchip CPU, it could scale to higher clock speeds than the Cyrix core could and had more level 1 cache, at the expense of no level 2 cache. The Centaur-derived VIA Cyrix III didn’t keep pace with an Intel Pentium III or an AMD Athlon but was very power efficient.

Speeds topped out at 800 MHz, using either a 100 or 133 MHz bus. The chips had 128 KB of L1 cache along with MMX and 3DNow instructions. VIA planned to reach speeds of up to 1 GHz, but that never happened with this generation of CPU.

Giving way to the VIA C3

VIA discontinued the Cyrix III in early 2001, after only about a year on the market. The successor the VIA C3, added 64K of level 2 cache and could reach speeds of up to 1.4 GHz. Yes, the C3 had more level 1 cache than level 2 cache. This is an unusual arrangement, but there’s no reason the level 2 cache has to be larger than the level 1 cache.

Neither the Cyrix III nor VIA C3 were competitive performance-wise with contemporary AMD or Intel CPUs. A VIA C3 running at 800 MHz couldn’t quite keep up with a Pentium III at 500 MHz. Even Transmeta did better than that. The FPU performance was even worse, with a Pentium III or Celeron beating the C3 by a factor of 4 at the same clock speed. Even as a budget CPU, Intel and AMD had the C3 beat, and VIA wasn’t undercutting them on price.

So you rarely saw a VIA Cyrix III or VIA C3 in a conventional PC. There just wasn’t much reason to put one there.

But VIA did have success selling the C3 into the embedded market, where power consumption was more important than raw performance. They also saw use in thin clients, another application where blazing speed wasn’t necessary.

From a retro perspective, these chips can be interesting since it’s sometimes possible to load DOS or Windows 9x on a thin client to turn it into a retro revival PC of sorts.

Why VIA could use Socket 370

VIA was the only company other than Intel to use Socket 370. It turned out that through several acquisitions, VIA came into possession of several patents Intel needed, which resulted in Intel and VIA agreeing to a patent cross license. This cross license expired in 2006 and Intel didn’t renew it, so the C3 disappeared from the market on March 31, 2006. VIA replaced it with a new CPU called the C7, then followed with the 64-bit VIA Nano in 2008. Neither the C7 nor the Nano ever competed with Intel or AMD as a mainstream CPU, but they’ve continued to exist on the edge of the market, presumably getting use in embedded systems. Some of the C7 CPUs used Socket 479 like a Pentium M, but VIA has also sold complete mini-ITX motherboards containing the CPU, chipset, and all other required supporting hardware.

Dave Farquhar

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.