Overclocking
Well, this is the part where I tell you about all of our marvelous overclocking exploits with the new, cool-running, die-shrunk processor—how we cranked it up 50% over its initial clock speed; how the Athlon XP now has more headroom than a convertible Buick; how our 3DMark scores shot up by hundreds of points with a few simple BIOS tweaks.

However, I can't do that.

I can't do that because the darned thing wouldn't overclock for us. Not by much, at least—not even by 100MHz. We were using mild bus speed overclocking, and we tried everything: core voltage tweaks, memory voltage tweaks, RAM timings more conservative than Gordon Liddy. Nothing helped enough to really matter.

At the end of the day, given the number of different ways we modified our system config and given the kinds of system crashes we were seeing, we could only come to one conclusion: the CPU just wouldn't go any faster than about 1.89GHz. And even at that speed, it was on the ragged edge.

Now, overclocking is never a sure thing. Every chip is different, and you never know what will happen when you run a chip out of spec. So I'd better not draw any conclusions from our one-off, isolated experience with our very first T-bred sample. I shouldn't speculate that AMD might be having trouble producing these chips with really good yields. And I really shouldn't wonder out loud whether the Athlon XP's 10-stage pipeline is hitting a snag at some point along the way that limits the chip's peak clock speed. Most importantly of all, I shouldn't mention the gossip I heard to that effect from other folks who had tested T- breds when I talked with them at Computex this past week. Especially not from engineers. I really, really shouldn't do that.

Still, I can't help but be a little bit worried about T-bred's prospects given my experience. Certainly AMD could refine its fabrication process or tweak the T-bred core with a new stepping or two and make these things hum—up to 2GHz and beyond. Right now, however, our sample of this newly die-shrunk processor is running right at its clock speed limit, only 66MHz above its peak speed on AMD's older fab process.

Conclusions
The benchmarks tell an interesting story. In some cases, despite all of its CPU and bus clock speed disadvantages, the Athlon XP is faster than any Pentium 4 processor. However, the Pentium 4 wins out in the majority of our tests. In many of the tests where the Athlon XP is slower than the P4, the 2200+ model's 66MHz clock speed increase doesn't deliver much more performance than the 2100+. Clearly, the Athlon XP's 266MHz front-side bus is a big bottleneck; it can't even keep up with the latest DDR333 memory, and DDR400 is already on the horizon.

Back when the Pentium III and Athlon were near the 1GHz mark, we saw this same problem: the Pentium III's clock speed hit a wall at 1.13GHz, and its slower bus just couldn't deliver extra performance from DDR memory. As a result, AMD took the performance lead and held on to it until the Pentium 4 came into its own. Now the tables have turned. The Athlon XP's bus is a bottleneck, and we're starting to wonder how well the chip will scale up to higher clock speeds. By contrast, the Pentium 4 is just getting started, and its newer design and platform give it a decisive edge. No wonder AMD has dedicated the bulk of its time and effort to bringing its K8 chip to market.

However, AMD has yet to relinquish the price-performance lead. AMD has led in this key category for ages, and given the Athlon XP's solid performance—even if it's not the fastest in every test—we've found it hard not to recommend an Athlon XP to just about anyone.

This time out, AMD is playing an odd game with its pricing. If you consult the AMD price list and then the Intel price list, you'll see that the Athlon XP 2000+ lists at the exact same price as the Pentium 4 2.0AGHz: $193. Though it's not yet listed there, the Athlon XP 2200+ will follow a similar pattern; it will be priced at $241, the same price at the Pentium 4 2.26GHz. AMD is matching its prices to Intel's using its model-number rating system as a guide.

That's a dangerous policy, since the Athlon XP isn't scaling up as well as the Pentium 4. Plus, the new P4 chips with 533MHz bus speeds are faster, clock for clock, than the 400MHz bus versions. In fact, AMD's model numbering scheme may need adjustment for future Athlon XP models. (I wish we'd have had time to benchmark the 2.2GHz and 2.26GHz variants of the Pentium 4 here today, so you could see a direct comparison between AMD's model number and Intel's clock speed. However, we were too busy with Computex this past week to make it happen.)

Left: Athlon XP Palomino. Right: Athlon XP Thoroughbred.

AMD really knows better than to price match Intel, however. If you check street prices on Pricewatch, for instance, you'll find that the Pentium 4 2.0AGHz is selling for somewhere north of $197, while the Athlon XP 2000+ is available for as little as $161. AMD seems to be applying a discount in reality, even if the price list doesn't reflect it.

Intel has its own discounts, too—especially for big system builders like Dell or HP. So if you plan on buying a pre-built PC, shop carefully. Of course, if you plan on doing that, well, ick. What are you thinking?

For those of us building our own boxes, the Athlon XP 2200+ is a pretty good value. However, if you're looking to overclock, you're probably better off with a lower speed grade of a Northwood Pentium 4, like the Pentium 4 1.6A. Those chips have a decent chance of hitting at least 2.13GHz on a 133MHz bus. If you're not looking to overclock, by all means, check out the Athlon XP 2200+. But you might want to look closely at our benchmarks before you make up your mind; which CPU is better depends quite a bit on how you're using it.