First post here, and I would like to add my 2 cents!
There has been debate to the blunder that AMD made by not getting the K5 FPU into the K6. Plain and simple, it would have been practically impossible and useless! I recall that by that time, FPU and (integer) CPU were no longer discrete entities running at asynchronous clock rates; The chips had had highly integrated designs that meant the FPU and the rest of the CPU were designed ground up to work together to minimize any bottlenecks in order to get peak performance. As people have stated in thread before: The K5 and K6 are very different designs in that the K5 had a pipelined FPU while the K6 had a low latency non pipelined FPU. It would not have made any sense, and is practically impossible. Add to that a few other points. 1) The K5 FPU would likely not scale to the clock rates necessary 2) During the K6's time, the Pentium II came along along and its FPU performance crushed anything before it making the K5 FPU performance a moot point.
In any case, during the times of the K5 and K6 were released, things were sure interesting in terms of CPU development.
At the time, only Intel was really focusing on FPU performance. Everyone else focused on integer performance. And then Quake 1 came out, followed by the slew of FPU dependant games ( I remember playing quake 1/quakeworld on a 486 DX4 120). Intel's Pentium, and later Pentium 2 really shone during that time. Everyone was caught off guard, and most CPU manufactorers began to fade away after that. AMD had a good chip with the K6 though. It was able to scale to high clock speeds (later as K6-2, K6-3, K6-2+) and it was a monster in terms of integer performance (The K6-3 could best the P2 and early P3 clock for clock in integer performance). In order to hold the fort untill it's own FPU monster was released, the K7, AMD developed the 3DNow! instructions.
Now I really don't know if the K6 was designed with future 3Dnow! instructions in mind... But it really seems like it did. No other CPU showed such a dramatic gain in performance with properly implemented SIMD instructions. 3DNow! brought K6 (2 or 3) performance parity with the P2 and P3 in some cases, and at a much lower cost, and it was not multiplier locked to facilitate easy overclocking! The Quake series of games good to the K6-2/3 in terms of performance. Recall that 3D accelerators came into prominance, and it was through 3DNow! optimizations of the video drivers that made the K6 line of CPU competetive with the P2 and P3 (Recall the miniGL driver for 3dFX, or the first Detonator drivers for the Riva TNT).
In any case, that is what I remember. A lot of factors and new technologies came into prominance. These factors helped the K6 series without the pipelined FPU survive untill the K7 was released.
