AMD K6-III
Last desktop Socket 7 processor with on-die L2 cache.
The AMD K6-III, code-named Sharptooth, arrived on 22 February 1999 as an x86 processor built on the K6-2 foundation. Its key addition was a 256 KB L2 cache integrated directly onto the chip, which boosted performance and let the existing motherboard cache serve as an L3 cache under AMD's TriLevel Cache scheme. It was the last desktop processor AMD officially made for the Socket 7 platform.
At launch, the K6-III went up against Intel's Pentium II and, soon after, the Pentium III. The 450 MHz version delivered integer performance that made it one of the fastest x86 chips available at the time, though its floating-point unit—inherited from earlier designs—fell behind Intel's parts in 3D games tuned for Intel architectures.
AMD stopped making the K6-III after introducing the Athlon, which took over its place in the product line. Later, low-power K6-III+ and K6-2+ models appeared, designed for laptops. They included PowerNow! power-saving technology and Enhanced 3DNow!, were built on a 180 nm process, and later gained a following among desktop enthusiasts and overclockers.
The design was conceptually straightforward: a K6-2 with 256 KB of on-die L2 cache. But implementing it required 21.4 million transistors. Its pipeline was shorter than the Pentium III's, which limited scalability past 500 MHz. Still, the K6-III 400 sold well, and the 450 MHz version was clearly the fastest x86 chip on the market at introduction, outperforming both K6-2s and Pentium IIs.
3DNow! was an AMD-developed extension to the x86 instruction set that added SIMD instructions for vector processing, improving performance in graphics-heavy applications. It debuted in the K6-2 in 1998. The K6-III+ brought Enhanced 3DNow! (also called Extended 3DNow! or 3DNow+), which added five new DSP instructions but not the 19 extended MMX instructions.
The original K6-2 had a 64 KB primary cache and a larger motherboard-mounted cache (typically 512 KB or 1024 KB). The K6-III, with its 256 KB on-die secondary cache, repurposed the external motherboard cache as an L3 cache, a setup AMD called TriLevel Cache. The L3 cache could reach up to 2 MB.
Intel's Pentium II replacement wasn't ready, so as a stopgap they released a modestly revised Pentium II rebadged as the Pentium III.
Quick Facts
- Produced-Start
- February 22, 1999
- Produced-End
- End of 2003
- Slowest
- 333
- Slow-Unit
- MHz
- Fastest
- 550
- Fsb-Slowest
- 66
- Fsb-Fastest
- 100
- Arch
- x86
- Microarch
- K6
- Predecessor
- K6-2
Facts from the source article.
Lore & Background
The K6-III was a K6-2 with on-die 256 KiB L2 cache, executed with 21.4 million transistors. Its pipeline was short compared to that of the Pentium III and thus the design did not scale well past 500 MHz. At its release, the K6-III competed with Intel's Pentium II and, shortly afterwards, the Pentium III. Its integer performance made the 450 MHz model one of the fastest x86 processors available at launch, although its inherited floating-point unit generally lagged behind Intel's processors in 3D games optimized for Intel architectures.
AMD chose not to sell a 500 MHz or faster K6-III after the rare 500 MHz K6-III had been immediately recalled; it was found to be drawing enough current to damage some motherboards. With the release of the Athlon, the K6-III became a low priority part for AMD—something to be made only when all orders for high-priced Athlons and cheap-to-produce K6-2s had been filled—and it became difficult to obtain in significant quantities. The original K6-III went out of production when Intel released their 'Coppermine' Pentium III.
Revised low-power K6-III+ and K6-2+ models, incorporating PowerNow! and Enhanced 3DNow! and manufactured on a 180 nm process, were designed for mobile computers but later became popular among desktop enthusiasts and overclockers. Both parts were die shrunk K6-IIIs (the 2+ disabled 128 KiB of cache, the III+ had the full 256 KiB) and introduced AMD's new PowerNow! power saving technology.
Reader's Guide
The K6-III's significance lies in its TriLevel Cache design, which repurposed the variable-size external motherboard cache as an L3 cache, allowing capacities up to 2 MB. This gave the K6-III a performance advantage over its predecessor and made the 450 MHz model the fastest x86 chip on the market at introduction. However, its short pipeline limited clock speed scalability, and production ended after the Athlon superseded it. The K6-III+ and K6-2+ variants, built on a 180 nm process, found an enthusiast following in desktop systems as some motherboard companies provided BIOS updates for their desktop motherboards to allow usage of these processors. These boards became firm favorites within the overclocking community, with K6-III+ and K6-2+ 450 MHz CPUs routinely overclocked to over 600 MHz. The K6-III's legacy includes being the last desktop processor for Socket 7 and a bridge to AMD's Athlon era.
Did You Know?
- The K6-III was the last desktop processor officially released for Socket 7.
- The 500 MHz K6-III was immediately recalled because it drew enough current to damage some motherboards.
- The K6-III+ and K6-2+ introduced PowerNow! power saving technology for mobile applications.
- The K6-III's 256 KB on-die L2 cache allowed the motherboard cache to function as an L3 cache in AMD's TriLevel Cache design.
More in Intel and AMD Microprocessors, Part 3 1-24
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