Performance prospects and model numbers
In addition to the Athlon 64 3800+ and FX-53 (939-pin edition), AMD is introducing two other chips: the 939-pin Athlon 64 3500+ running at 2.2GHz with 512K of L2 cache, and the Athlon 64 3700+ intended for Socket 754, with a 1MB L2 cache and a 2.4GHz clock speed.

Confused yet? If so, you're probably not alone. AMD's model numbering methods continue to elude me. Prior to the introduction of these chips, I had thought that AMD was using clock speed increments and cache sizes in a fairly predictable way: adding or removing 200MHz in clock frequency would move the model number up or down by 200, as would the transition from 512K of L2 cache to 1MB (or vice versa). Thus, the Athlon 64 3000+ runs at 2.0GHz with 512K of L2 cache, while the Athlon 64 3200+ runs at 2.0GHz with 1MB of L2 cache. The Athlon 64 3400+ also packs 1MB of L2, but clocks in at 2.2GHz. All neat and logical, right?

In fact, early speculation about Socket 939 chips suggested AMD would use the addition of a second memory channel interchangeably with the cache size and clock speed increments, so that an Athlon 64 clocked at 2.2GHz with 512K of L2 cache and dual-channel memory would earn the rank of 3400+. That would be the neat and logical thing to do, but such is not the case. Instead, AMD has called that product the 3500+. And just to make things more confusing, the new Socket 754 chip that differs from the Athlon 64 3400+ in nothing but 200MHz of clock frequency has been dubbed the 3700+!

What's changed? Well, perhaps that mythical Athlon "Thunderbird" processor, against whose performance at a given clock speed the model numbers for all subsequent Athlon products are purportedly determined, hit a performance scaling problem at 3.5GHz in AMD's secret labs. Har har. But the more obvious culprit is Intel's Pentium 4 "Prescott" processor, which delivers less performance, clock for clock, than previous Pentium 4 chips. No doubt AMD has tweaked its numbering formula to aid comparisons with the latest Pentium 4s.

To help you navigate these troubled waters, let me present to you a partial guide to AMD "Hammer" model numbers, which I cooked up one night while trying to make sense of it all.

It all looks sensible when laid out that way. Until you really think about it.

So what kind of performance can we expect from these new chips? Well, we've already reviewed the Athlon 64 FX-53 in its Socket 940 form, and we know that it's stinking fast. The move to Socket 939 shouldn't change the math too much, but a couple of factors may work in its favor to some degree. Switching to unbuffered DIMMs should cut memory access latencies ever so slightly. That's always a good thing.

As for the 5X multiplier on the HyperTransport link, its benefits may be difficult to spot. Juicing up HyperTransport—to a new peak of 8.0GB/s at an effective 2GHz clock rate—is a forward-looking move that will probably pay off when PCI Express arrives. This link serves as the Athlon 64's connection to the rest of the system, but with the memory controller onboard the CPU, the HyperTransport link isn't particularly burdened in current systems. Our review of the VIA K8T800 Pro chipset showed us few instances where faster HyperTransport seemed to register in the benchmark scores.

You can compare the Socket 940 version of the Athlon 64 FX-53 to the 939-pin version when reading our benchmark results, but you need to know a secret code to do it. That secret code is this:

Opteron 150 = Athlon FX-53 (940-pin version)

These two products are essentially the same thing with different names, with the notable exceptions that the Opteron name is more respectable in proper computing circles, while the FX-53 has an unlocked multiplier for us disreputable overclockers to tweak. The performance is identical, so long as there's no overclocking at work. I've left the Opteron 150 label on our graphs because, well, that's what I used in testing.

The Athlon 64 3800+ is just an Athlon 64 FX-53 minus 512K of L2 cache. Sometimes, its smaller cache will slow it down a little bit, but other times, the 3800+ should run neck-and-neck with the FX-53. All depends on whether the application is able to use the FX's extra L2 cache to its advantage.

But enough gabbing. Let's see the numbers.