AMD Duron 750

When we were first introduced to AMD's Duron, it renewed our faith in the recent axiom: value doesn't have to mean slow. Originally introduced to us by Intel's Celeron, the idea of "value" CPUs coming dangerously close in performance to their counterparts in the performance desktop market segment has been one that we have hung on to ever since.

One thing we learned from our experience with the Duron was that because of its very close ties to the Athlon (same FSB and same memory bus), the Duron has no problem competing with the Celeron in terms of performance. In fact, it took an overclocked Celeron running at 850MHz, a clock speed that the Celeron won't hit until sometime next year, to come close to the performance of a normally clocked Duron running between 600 and 700MHz.

The reason Intel is falling behind, performance-wise, in the value market segment is because the Celeron is being horribly crippled by its 66MHz FSB and 66MHz memory bus. Giving the Celeron 100MHz FSB support would definitely help it perform closer to the levels that we saw with the first Durons, however it still lacks something, which is hindering its performance.

As we discovered in our original review of the Celeron, there were obviously a number of factors that contributed to the Celeron performing slower than the Pentium III on a clock for clock basis. The most noticeable reason was the fact that the Celeron only ran at a 66MHz FSB and was thus limited to a 66MHz memory bus (on BX boards), but even when overclocked using a 100MHz FSB setting, the Celeron was still coming in well below an equivalently clocked 100MHz FSB Pentium III.

It turns out that the missing link was the L2 cache subsystem of the Celeron. As you all know, the Celeron features exactly 1/2 the L2 cache of the Pentium III (128KB vs. 256KB). The way Intel apparently produces the Celeron is by taking the Pentium IIIs that may have a number of bad cache blocks during their production and effectively disabling half the cache.

This explains why the Celeron has an identical transistor count to the Pentium III in spite of having half the L2 cache (cache increases transistor count dramatically) and it also explains why the Celeron's L2 cache is only a 4-way set associative L2 cache while the Pentium III features an 8-way set associative L2 cache.

This difference in cache mapping does create a noticeable performance delta between the two chips; for a more thorough explanation on the reasons behind this, take a look at our comparison of cache mapping techniques in our AMD Thunderbird Review.

With those factors all hurting the performance of the Celeron, it isn't surprising that the Duron is able to dominate it in virtually all aspects. And today, the Duron even surpasses the Celeron in terms of clock speed as well. Now running at 750MHz, the Duron has an additional selling point that OEMs and system integrators can push: clock speed advantage. While most AnandTech readers know that operating frequency is only as important as the CPU that's running at that speed, your average buyer is only going to compare various systems based on a handful of specifications, including clock speed.