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The 975X chipset: Intel does dual graphics
The 975X pairs up a revamped north bridge with the familiar ICH7R south bridge I/O chip.

A block diagram of the 975X chipset. Source: Intel.

The only notable change between the older 955X chipset and the new 975X is that the 975X can slice up its 16 lanes of PCI Express dedicated to graphics into a pair of eight-lane connections for use in dual-graphics schemes. ATI's CrossFire and S3's DuoChrome will support the 975X, but NVIDIA apparently intends to maintain a driver-based lockout that will limit SLI to its own nForce4 chipsets. This development comes as something of a surprise, since rumors were circulating widely about NVIDIA supporting SLI on the 975X, and even some of the initial communications we received from Intel about the 975X mentioned SLI support. NVIDIA has long claimed that it would validate third-party hardware for SLI if the hardware were submitted to its SLI validation program. We recently learned at CES that Intel and its motherboard partners have submitted 975X boards for validation, and we also learned that NVIDIA is not likely to validate those boards for SLI. We also got the distinct impression that NVIDIA's refusal to validate the 975X is almost certainly not motivated by technical problems, especially given the fact that the initial SLI demo systems were based on Intel core logic chips.

Intel says it's still working on getting SLI validation for the 975X, but I wouldn't hold my breath waiting for it. Perhaps if Intel agrees to certify nForce chipsets for its Centrino or Viiv platforms, NVIDIA will open up SLI support on the 975X. Turnabout is fair play, right?

Thermal problems?
Regular readers may recall that our review of the Pentium Extreme Edition 955 was delayed by thermal problems, as we've explained. Intel claims the problems we experienced—with two separate kits consisting of a motherboard, CPU, and cooler—are still something of a mystery. The problem was resolved by switching to a third-party cooler with a different retention mechanism, and our current best guess is that the trouble we encountered was related to the CPU cooler retention mechanism. This possibility was first suggested to us by Chris Angelini, another reviewer who had encountered similar problems. Chris speculated that the CPU cooler might be tensioned too tightly, causing the Intel D975XBX motherboard to warp and thus preventing the cooler from making clean, even contact across the surface of the CPU. This theory would seem to explain why we saw relatively better (though not entirely satisfactory) results when using the cooler's included TIM pad on initial installation of the CPU rather than thermal grease.

Whatever the case, we don't believe the CPU itself was at fault. The Extreme Edition 955 pulls less power and thus dissipates less heat under load than its predecessor, the Extreme Edition 840, as our test results will show. Intel may have larger problems with its LGA775 thermal infrastructure, though. We'll have to keep an eye on this issue.

AMD's FX flagship doubles up
So Intel has chopped its dual-core product up into two chips, doubled the L2 cache, raised the clock and bus speeds, and performed a die shrink to 65nm. AMD's response is much simpler than all of that. The Athlon 64 FX-60 is pretty much just an Athlon 64 X2 4800+ blessed with a 2.6GHz clock speed and a fancy name.

The Pentium Extreme Edition 955 (left) and Athlon 64 FX-60 (right)

This simple move represents a major transition, though, because AMD's high-end gaming CPU is at last making the leap to dual cores. The FX-60 gives up 200MHz to the Athlon 64 FX-57, but its second core should benefit from the introduction of multithreaded graphics drivers by both ATI and NVIDIA. In fact, AMD is saying that the Athlon 64 FX-57 may be the last of its high-speed, single-core processors. The FX-57 will exist alongside the FX-60 for the time being, allowing consumers to choose between a single 2.8GHz core or the equivalent of two Athlon 64 FX-55 cores in the FX-60.

Like all dual-core AMDs to date, the FX-60 is a 90nm chip. AMD has yet to make the transition to 65nm, but continues to claim that its transition to 65nm is "on track." For now, AMD will have to rely on its current mix of CPU microarchitecture and 90nm SOI manufacturing capabilities to deliver an attractive performance per watt proposition. We'll have to see whether the FX-60 can match the 65nm Presler there.

The match-up
That brings us to the main event, the match-up between the FX-60 and the Extreme Edition 955, which is rife with subplots. The biggest question, of course, is which of these high-dollar CPUs can claim to be fastest, and the natural follow-up will deal with power consumption as it relates to performance. Beyond that, we'll want to keep track of several other notable questions.

We expect some sort of a boost from multithreaded graphics drivers (we'll be testing with NVIDIA's), but how much and what sort of performance gains? NVIDIA has said that it will offload some vertex processing to the CPU in these drivers, and so we should expect to see gains at lower resolutions, where vertex throughput is more likely a bottleneck than graphics pixel-pushing power. Fortunately, we already tend to test CPU gaming performance at lower resolutions precisely because we don't want graphics fill rates to become a bottleneck. Then again, the performance gains from multithreading in the graphics driver aren't likely to be huge. Can dual-core CPUs really take advantage of multithreaded drivers well enough to outpace faster single-core processors in otherwise single-threaded games? For that matter, can the single-core Pentium 4 Extreme Edition 3.73GHz capitalize on its Hyper-Threading abilities to become more competitive with the Athlon 64 FX-57 in 3D games?

In a similar vein, we've tested largely with 64-bit applications on Windows XP Pro x64 Edition, and many of those applications are multithreaded. We'll be interested to see how newer 64-bit code and multithreading affect performance on different CPU microarchitectures.