The K6: AMD Extends Its Range
In 1997, AMD released a new processor: the K6. Unlike the K5, which was created by AMD, the K6 was the result of the work done by NexGen on the Nx686. This processor was compatible with Socket 7 (Pentium) motherboards and offered very good performance compared to Intel’s Pentium II processors, at a much lower price. The K6’s FPU was still a little weak compared to Intel’s. A 250 nm version of the K6, called Little Foot, came out in 1998.
Also in 1998, AMD announced the K6-2, a processor that used a faster bus (100 MHz) and had improved SIMD performance. It also had one more MMX unit than the K6 and a new instruction set, 3DNow!, for floating-point calculations (MMX handled only integers). The K6-2 (400 and up) was a big success because it was a good upgrade solution for owners of Pentium MMX platforms—by using the 2X multiplier on a motherboard with a 66 MHz bus, the processor was in fact operating at 6X (400 MHz), which permitted a significant gain in speed at a lower upgrade cost.
Finally, in 1999, AMD released the third version of the K6, the K6-III. The main difference from the K6-2 version was an on-chip 256 KB cache. The K6-III was very fast, but also very costly to produce, and was quickly replaced by the Athlon (K7).
| Code name | K6, Little Foot (250 nm) | K6-3D, Chomper | Sharptooth |
| Date released | 1997/1998 | 1998 | 1999 |
| Architecture | 32-bits | 32-bits | 32-bits |
| Data bus | 64-bits | 64-bits | 64-bits |
| Address bus | 32-bits | 32-bits | 32-bits |
| Maximum memory | 4,096 MB | 4,096 MB | 4,096 MB |
| L1 cache | 32 KB + 32 KB | 32 + 32 KB | 32 + 32 KB |
| L2 cache | motherboard (FSB frequency) | motherboard (FSB frequency) | 256 KB (CPU frequency) |
| L3 cache | no | no | motherboard (FSB frequency) |
| Clock frequency | 166-300 MHz | 300-550 MHz | 400-450 MHz |
| FSB | 50-66 MHz | 66-100 MHz | 100 MHz |
| FPU | built-in | built-in | built-in |
| SIMD | MMX | MMX, 3DNow! | MMX, 3DNow! |
| Fabrication process | 350 - 250 nm | 250 nm | 250 nm |
| Number of transistors | 8.8 million | 9.3 million | 21.3 million |
| Power consumption | 12-28 W | 13-25 W | 10-17 W |
| Voltage | 2.2–2.9 V–3.2 V | 2.2–2.4 V | 2.2–2.4 V |
| Die surface area | 157-68 mm² | 81 mm² | 118 mm² |
| Connector | Socket 7 | Socket 7 / Super Socket 7 | Super Socket 7 |
AMD also marketed K6-2+ and K6-3+ processors, mainly for portable PCs. These used a 180 nm fab process and had an on-chip 128 KB (K6-2+) or 256 KB (K6-3+) L2 cache.