Our tests have shown that quad-core systems can offer substantial performance gains in a broad range of applications, if the computing problem lends itself to parallel processing and if developers put the necessary effort into making their software multithreaded. Such widely multithreaded programs are not common today, especially among traditional consumer-oriented desktop applications. Even some creative tools intended for parallelizable tasks, like QuickTime Pro, use a maximum of two threads at present. Top developers like Valve are working on making their applications take advantage of four or more cores, though, and they will likely pave the way for the rest of the industry.
When those applications do arrive, we probably shouldn't expect to see a general doubling of performance when moving from two cores to four, or even the same degree of performance leap we saw when going from one core to two. That's not what we've seen from most of these widely multithreaded applications. The reasons for this scaling difficulty are many, but they are summarized in Amdahl's Law. The degree of speedup we can expect will depend on the nature of the application, the skill of the programmers, and the other constraints of the hardware.
Between the two quad-core systems we tested, the Core 2 Extreme QX6700 is faster overall. The Quad FX system with a pair of Athlon 64 FX-74 processors puts up a surprisingly good fight, though, thanks to its relatively high clock speed and superior system architecture. At the very least, the overall performance title is no longer unified due to the strength of Quad FX's showing. By adapting its dual-socket workstation platform for the desktop, AMD has shown that it can still offer very competitive performance, so long as you don't mind the power consumption that comes with it.
I'm pleased that the original 4x4 concept has been moderated so that it's no longer tied to pairs of extremely pricey CPUs, no longer exclusive to vendors of outrageously expensive PCs, and no longer mated with quad-GPU graphics. Those adaptations have transformed Quad FX from a gimmick into a potentially attractive platform and a welcome development for PC enthusiasts.
Unfortunately, the Quad FX concept hasn't entirely escaped its roots in excess and exclusivity. Most notably, the Asus L1N64-SLI WS is too expensive, and it raises the overall cost of the platform. The mobo's price tag, size, and power consumption are no doubt higher due to its use of dual core-logic chips, which is probably an artifact of 4x4's original quad-GPU associationand is just silly. The fact that this Asus board is the only Quad FX option makes it more of a problem. If this were one choice among many, we could more easily accept it as a part of the picture and move on to more reasonable alternatives.
Quad FX also suffers from a lack of low-power or even mid-power CPU options, which is a shame. This same technology in Opteron form offers a very compelling power efficiency proposition compared to the competition from Intel. Quad FX could do the same, if AMD would let it. Bring on the pairs of Athlon 64 X2 5200+ Energy Efficient processors and single-chipset motherboards with dual PCIe x16 slots, please, AMD. Then, trust me, you will have our attention.
For now, though, Intel's quad-core processors offer better performance, lower power draw with correspondingly lower fan noise, and a range of excellent motherboard choices, almost all of which will fit into a standard ATX enclosure. Perhaps what AMD needs most is to make the transition to 65nm chip fabrication technology, so that quad-core computing doesn't require an additional socket.