AMD Athlon 64 FX-74 review

Since Intel wheeled out its new Core 2 processors last summer, it's been a bruising time for AMD. If the clear advantage in performance and power consumption parsimony of Core 2 in dual-core trim wasn't bad enough, Intel unsheathed the quad-core Kentsfield revision, piling on more pain. Something had to be done.

That something is Quad FX, AMD's new dual-socket desktop computing platform. Of course, the philosophy behind Quad FX is simple. Unable to match Intel's quadcore killer in a single CPU package, AMD did the next best thing: a pair of dual-core chips in two sockets.

AMD already has multi-socket processor technology - the Opteron workstation and server class CPU. It's essentially the same CPU core design as the desktop-bound Athlon 64 chip but with added wiring for symmetric multi-processing.

So, is Quad FX merely a rebadged Opteron platform for the desktop? Not exactly. It does leverage the latest 1207-pin LGA Opteron socket. But in discarding the need for slower and more expensive registered ECC memory, in favour of unbuffered DDR2 DIMMs at speeds of up to 800MHz, AMD has ensured Quad FX is much more mass-market friendly.

The processors themselves are essentially the same as existing Athlon 64 X2 chips and are available in three trim levels, kicking off at 2.6GHz for the FX- 70 and topping out with the FX-74 in 3GHz, the highest speed bin yet for a dual-core AMD CPU. For now, Quad FX chips will be sold in matched pairs. A brace of FX-74s is yours for £600 or so.

Multi-core scaling

On paper, Quad FX is a powerful platform. It promises an advantage in one key area of performance: multicore scaling. Intel's current quad-core Kentsfield chip is nothing more than a pair of Core 2 dual-core chips crammed into a single CPU package and sharing a single processor-to-motherboard-chipset bus - so many of the tweaks Core 2 contains, which address the weaknesses of its half-duplex 1066MHz front side bus, are compromised.

Quad FX, by contrast, benefits from AMD's so-called direct connect technology in the form of a 2GHz Hypertransport link between the two CPU sockets. In broad terms, AMD and Intel's quadcore solutions are more similar than they first appear - and it's actually AMD's approach that offers superior die-to-die bandwidth and latency.

Add in the modest 200MHz frequency bump AMD has delivered with the new Athlon 64 FX-74 processor and you have a recipe for an intriguing quad-core contest with Kentsfield. But as our benchmark results demonstrate, even with theoretically superior multi-core communications and a 300MHz frequency advantage, Quad FX cannot match the performance of the Core 2 architecture.

There are issues involving the way Windows XP handles the Quad FX system memory architecture that are expected to be solved by Vista. But disappointing performance is just the start. It's hard to see why anyone would prefer a power hungry, expensive dual-socket solution.

And it suffers from the same existential crisis as all quad-core desktop solutions - few applications can make use of more than two CPU cores. The only upside we can see is the arrival of AMD's own native quad-core chip later this year.