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A quick look at AMD's 65nm Athlon 64 X2 processors

Energy efficiency and overclocking headroom explored

AMD HAS BEEN PROMISING for some time to deliver chips made on its 65nm fabrication process by the end of 2006. The year's end is perilously close, but a small package arrived at Damage Labs last week bearing evidence of AMD's success: a pair of 65nm Athlon 64 X2 processors. Looks like they've just made it in under the wire. In fact, Athlon 64 X2 processors built in this 65nm process are filtering out into the market now.

Process shrinks often bring with them some nice benefits, because smaller chips tend to require less voltage, consume less power, and generate less heat. They also sometimes allow more headroom for clock frequency increases. The question is: how is AMD doing on these fronts? What benefits does its 65nm process bring to the Athlon 64 X2? Let's have a look.

The Athlon 64 X2 at 65nm: Less of the same
First things first: the Athlon 64 X2's conversion to 65nm is a die shrink and not much more than that. AMD says these chips ought to perform just like their counterparts at 90nm, so one shouldn't expect any notable performance improvements. The company does have microarchitectural improvements planned for its so-called "K8L" design, which is expected to debut around the middle of next year.

Between now and then, AMD will reap two main benefits from this conversion. First, the chips themselves are smaller, down from 183mm² at 90nm to 126mm² at 65nm. The 65nm and 90nm versions share the same estimated transistor count of 153.8 million. Second, these processors are manufactured exclusively at AMD's Fab 36 facility using 300mm wafers. These wafers have 2.25 times the area of the 200mm wafers produced at AMD's adjacent Fab 30 facility. Taken together, the smaller chips and larger wafers should make for much lower per-chip production costs, provided AMD is able to get good yields out of its 65nm process. That cost savings is especially crucial because Intel has had multiple fabs producing 65nm chips on 300mm wafers for quite some time now.

A pair of 65nm Athlon 64 X2 processors

The two 65nm Athlon 64 X2 processors we received for testing are the 4800+ and 5000+ models, both intended for Socket AM2 motherboards. Although nothing much has changed in terms of CPU performance at 65nm, the transition gives AMD an opening to jack with its CPU model numbers, and of course, it didn't let the opportunity pass without action. These processors have the ability to support half-step multipliers, so clock frequencies can now be controlled in 100MHz increments. Combine this ability with AMD's apparent determination to kill off or at least significantly reduce the number of Athlon 64 X2 processors with 1MB of L2 cache per core, and you have a recipe for a substantially revised set of model numbers. The new lineup of Athlon 64 X2 models at 65nm looks like so:


Clock speedL2 cache
(per core)
Athlon 64 X2 4000+2.1GHz512KB65 W$169
Athlon 64 X2 4400+2.3GHz512KB65 W$214
Athlon 64 X2 4800+2.5GHz512KB65 W$271
Athlon 64 X2 5000+2.6GHz512KB65 W$301
Before it was canceled, AMD offered an Athlon 64 X2 4800+ (at 90nm) with 1MB of L2 cache per core and a 2.4GHz clock speed. Now, the 4800+ model number is back, inhabited by a 2.5GHz processor with 512K of L2 cache per core. Cache size and clock frequency don't always affect performance in the same way, or equally, but I doubt most folks will lose any sleep over these differences.

Notice that all of the Athlon 64 X2 chips at 65nm have a thermal design power (TDP) rating of 65W, down from 89W for standard-issue Athlon 64 X2s at 90nm. The range of recommended core voltages is also lower, from 1.30-1.35V at 90nm to 1.25-1.35V at 65nm. Due to the lower TDP rating, these processors get the same "Energy Efficient" label that AMD previously reserved for specially manufactured 90nm parts. So the full, official name of the 5000+ CPU we're testing is "Athlon 64 X2 5000+ Energy Efficient," burdened with four last names like a second-generation feminist. (What was that, Mr. Snerdley?) Fortunately, none of the 65W Energy Efficient models carry a premium any longer, so the 65nm parts are priced identically to their 89W/90nm counterparts.

A trio of late 90-nano additions, too
We'd be remiss not to point out the addition of a few new 90nm models to the Athlon 64 lineup, as well. AMD has stealthily slipped these into its product mix, just below the Athlon 64 FX-62 and just above the 5000+. They are:


Clock speedL2 cache
(per core)
Athlon 64 X2 5600+2.8GHz1MB89 W$505
Athlon 64 X2 5400+2.8GHz512KB89 W$485
Athlon 64 X2 5200+2.6GHz1MB89 W$403
Yes, you're looking at two new Athlon 64 X2 models with 1MB of L2 cache per core. I won't pretend to understand AMD's strategy here, which seems to involve confusing the customer, then conquering him. The most confusing model of the bunch may be the 5600+, which shares the same cache config and clock speed as the Athlon 64 FX-62, but lacks the FX-62's unlocked upper multiplier. The 5600+, though, has an 89W TDP, while the FX-62's is 125W. And the 5600+ costs over $200 less than the FX-62. Go figure.

Unfortunately, we don't have any samples of the 5600+, 5400+, or 5200+ for testing, so that will have to wait for another day.