Review: AMD Athlon64 FX-51

Thoughts and musings

Limited frequency headroom forced AMD into designing a CPU that could do more for a given clock speed and scale higher than the current Barton core. This wasn't a decision taken a few months ago on a whim, it was an ambitious project started many years ago. AMD's been playing a naming game of late. The Opteron CPU, love or loathe the name, showed its strengths when unveiled in April. Happily running in a uniprocessor system for workstation-class application, or residing in an 8-way 64-bit server full of architectural niceties such as HyperTransport links to one another, compatibility with existing 32-bit code, independent memory pools, and scalable bandwidth made it a decent choice for midrange business. AMD has now sought to extend the Opteron's usefulness to the home consumer market. The Athlon64 FX-51 is currently AMD's top-of-the-range consumer-orientated CPU. Don't be put off by its meagre 2.2GHz clock speed. With most of the benefits that the Barton XP3200+ currently enjoys and clever engineering, encompassing on-die memory controllers, SOI manufacturing, larger, more efficient L2 cache, SSE2 instruction sets and a plethora of other performance-enhancing extras, the FX-51 has taken a sledgehammer (sorry, bad joke) to the present Barton XP3200+'s performance.

Performance, it seems, is truly excellent for a processor that's still knee-deep in x86 32-bit architecture, yet the same CPU also has to ability to effortlessly morph into a 64-bit CPU and all the benefits that larger memory addressing and optimising creates. 64-bit, whilst being one of the fundamental advances put forward by AMD, is not really applicable to home users yet. We'll have to wait for compliant OS's and drivers before we can judge its effectiveness. That's one of the FX's strong points. It's great now, and it promises to be great in a year or two's time. Our 32-bit benchmarks showed that the FX-51 has the beating of any current 32-bit CPU, including Intel's finest. It's kind of awe-inspiring to see just what kind of dent it puts into the P4's armour. Make no mistake about it, the Prescott needs to be a fantastic CPU if it's to wrestle the performance crown away from the FX-5x series, and it can forget about challenging in the 64-bit arena. The major drawback, as far as enthusiasts are concerned is in the use of registered memory. Let's not forget that AMD is positioning the FX-5x as a high-end uniprocessor, workstation-class CPU, as well as a mighty fast home CPU. But we're adamant that all the usual suspects will soon find themselves marketing high-speed matched ECC memory. Scaling ought to be better than the current Barton's, courtesy of a longer pipeline, but the 1MB L2 cache may limit overclocks to some degree. We'll find out as users chime in with their results.

There's lots of good in the FX-51, that much is plainly clear. AMD's technical team have done an outstanding job. The same praise cannot be fairly levelled at the P.R team. We're adamant that the vast majority of consumers will find it hard to differentiate between the various Opteron clones. There's the 1xx Opteron series, there's the FX-5x series, there's also another derivative with a single-channel memory controller; that's the Clawhammer, folks, and it doesn't use registered memory - yay. But wait, there's also destined to be a 939-pin non-ECC FX CPU that uses ordinary, unbuffered DRAM. Hell, we're confused thinking about it. Confusion is a problem that may be alleviated via sensible education, but with a die size of no less than 193mm², the FX CPUs will come to market with enormous price tags. Perhaps the jewel in the enthusiasts' crown will be the cheaper 754-pin Clawhammer - who knows.

It's difficult to ascertain the 64-bit qualities of the FX-51 right now. Limited OS support and limited driver support make any tentative benchmarking perilous. I'll leave that up to Mr. Technical, a.k,a Ryszard. What we can say, though, is that in 32-bit mode, the Athlon FX-51 currently has no performance peer. Thanks to a number of sensible core improvements, of which an on-die memory controller, larger L2 cache and SSE2 support are notable, especially with respect to gaming. The AMD Athlon64 FX-51 is a force to be reckoned with. It'll be hugely expensive, but that's kind of expected. We'd put our money on a cheaper model in the hope of overclocking it to FX-51 levels and above. We can't recommend the FX-51 solely due to its mammoth price, which is reckoned to be around £700, but if you want the fastest x86 CPU going, this is it.