Pushing the core to 750MHz
From our testing with overclocking the Athlon, we found that hitting the 750MHz mark on the current Athlon core posed a small but navigable obstacle. The way we got around it in our tests was to simply bump up the core voltage from the default 1.60v to around 1.70v or above. The problem with this approach is that it isn't a very elegant way of paving the way for an increase in clock speed, and we didn't expect AMD to do the same with the Athlon.
If you recall from our original Athlon review, the Athlon core is a 22 million transistor monster that is built around a 0.25-micron die fabrication process, referring to the size of the circuit itself. Obviously, pushing the clock speed of the Athlon to 750MHz generates more heat than all of the previous Athlon clock speeds, and in order to gain high enough yields on the CPU without simply bumping up the rated core voltage, AMD felt that making the move down to a smaller process would be the best avenue of approach.
The migration down to a 0.18-micron process helps to shrink the size of the Athlon's die and decrease the generation of heat, as well as the power consumption of the CPU itself. The latter was actually a very large problem with the original Athlon because a large strain was placed on motherboards and power supplies not capable of supplying the system the current it needed to operate properly.
Thus, by looking at AMD's roadmap and the analysis we published right after Comdex, the introduction of the Athlon 750 is actually the introduction of the new K75 core that we talked about in that article. The K75 itself isn't much different from the K7 core; physically, it is a smaller die (102 mm^2 K75 core vs. 184 mm^2 K7 core) as a result of the 0.18-micron fabrication process but other than that the performance and features are identical.
The K75 core put to use on the Athlon 750 will be with the Athlon throughout the first half of 2000. While it will eventually take on an on-die L2 cache, the core itself won't be modified until the second half of 2000 when the enhanced K75 core is introduced in the codenamed Mustang CPU.
In summary, the move to a smaller 0.18-micron process has enabled AMD to hit the 750MHz mark flawlessly. A similar move was made by Intel with their Pentium III E CPUs (Coppermine) just one month ago. In both cases, the move was made seamlessly and there are no signs of keeping yields up on the CPUs.