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AMD's Athlon XP 2200+: Thoroughbred unbridled

How fast can this Thoroughbred run?

THE GREAT GIVE-AND-TAKE battle between Intel and AMD for performance dominance in desktop processors took a decisive turn recently with the introduction of new chipsets for the Pentium 4 (and the corresponding P4 processors) that support a 533MHz front-side bus speed. That move, combined with a further ratchet of the Pentium 4's top clock speed to 2.53GHz, gave Intel a decisive advantage over AMD—the biggest such lead for Intel in quite a while, in fact.

Intel's processors have benefited greatly from the die shrink that happened back in January when the "Northwood" P4s first hit the scene. Built using Intel's 130nm manufacturing process, Northwood runs faster and cooler than the original "Willamette" Pentium 4, even as it packs in 512K cache—double the amount in its predecessor. Since the Northwood arrived, processor watchers have been waiting impatiently for AMD to counter with a 130nm CPU of its own, a version of Athlon XP code-named "Thoroughbred." It's taken some time, but T-bred is finally here, running at 1.8GHz and given an AMD model number of 2200+.

But is T-bred swift enough to catch one of Intel's 2.4 or 2.53GHz burners? Let's take a closer look.

Thorough breeding
Let's dispel the rumors right now. Thoroughbred is simply a die shrink of the Athlon XP. Nothing more. Well, OK, not much more. AMD says T-bred's transistor count is 37.2 million, down a smidgen from the previous "Palomino" version of the Athlon XP, due to a more efficient layout and "lower voltage handling requirements." That explains why the T-bred is a different shape than Palomino, too. But T-bred doesn't include any notable performance tweaks like more cache, SSE2 instructions, or other sorts of engineering magic. The die shrink means the Athlon XP ought to be able to reach much higher clock speeds in the future, but clock for clock, a T-bred ought to perform exactly like a Palomino.

Not only that, but AMD is not yet—if ever—raising the Athlon XP's front-side bus speed from its present speed of 266MHz. So Athlon XPs—of any flavor—will be hard pressed to take full advantage of advances in memory performance like DDR333 or dual-bank memory controllers.

Of course, none of these things mean, all by themselves, that the T-bred won't be a screamer. The Athlon XP has scaled up fairly linearly in performance to date, and only the benchmarks will tell whether how well T-bred fares in that department.

We'll get to benchmarks in a moment, but let's consider T-bred's other virtues. As you might expect with a die shrink, T-bred should be smaller, run cooler, and suck up less voltage than the Palomino. The 2200+ version requires only 1.65V, while the 1700+ needs just 1.5V. (All Athlon XP models, from 1700+ up, will transition to the T-bred core.) In fact, AMD allocated its first, limited supplies of production T-breds to computer makers for use in laptop PCs.

But the size difference is T-bred's most striking attribute. Have a look at the difference between a Pally and a T-bred:

Throughbred's on the left, and Palomino's on the right

T-bred is clean underneath because the resistors have moved up top

T-bred is downright teeny. To my eye, it's nearly half the size of the Palomino. The shrink from 180nm to 130mn is major. Officially, T-bred is 80 mm2, while Palomino is 128 mm2. By contrast the Pentium 4 is absolutely mammoth. Early Northwoods packed all 55 million of their transistors into a space 145 mm2, while ongoing process tweaks have cut the size on newer chips down to 131 mm2, according to reports.

(Also, in case you're wondering, AMD hasn't abandoned its plans to move its CPU packages from brown, like you see here, to green, like you can see here. Apparently the color change is just taking some time, and the Athlon XP 2200+ sample we received from AMD just happens to be brown. Eventually, minty-fresh green will engulf the entire Athlon XP lineup.)

A 'bred in the hand... Erm. Sorry.

Of course, all of this shrinkage action has a purpose. The smaller the chips, the more chips AMD and Intel can manufacture per wafer. More chips per wafer means lower manufacturing costs, and ultimately, lower prices, too. AMD's size advantage here is formidable, which ought to translate into a competitive advantage. However, Intel pulled a new trick out of its bag recently: it increased the size of its wafers from 200 mm2 to 300 mm2, and there's some debate over who has the advantage in terms of manufacturing costs as a result. Whatever the case, know this: a processor price battle is coming. The latest round of price cuts has already gone mighty deep, and there's more looming on the horizon.

Well, OK, maybe not looming on the horizon. More like hanging out over there, waiting to throw us a little party later on. With free beer and little cheese wedges with toothpicks in them. I can't wait.

AMD should also be able to keep overall Athlon XP system costs down, because T-bred doesn't require a new Socket or, by and large, even a new motherboard design. Usually a BIOS update will suffice; even some old KT133A boards will work with T-bred, though I'm not sure I see the point of that. AMD is quite proud of the relative stability of its Socket A platform in this respect.

Personally, I'm happy for them and everything, but I'd rather have a faster front-side bus than a killer (or probably overkill) CPU upgrade for my KT133A rig.