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Intel's P4 XE 3.46GHz processor and 925XE chipset


October surprise
— 12:01 AM on November 1, 2004

WHAT CAN I SAY about the Pentium 4 Extreme Edition processor? It's a stranger in a strange land, an anomaly in the desktop processor world, a thousand-dollar CPU inhabiting a world of sub-$1K computers. The technology comes from the Intel's high-end server products, a Xeon processor core dubbed Gallatin with 2MB of on-chip L3 cache.

Le-vel-three.

That's in addition to the L1 and L2 caches you'll find on normal Pentium 4s. Not only that, but the Extreme Edition is based on older technology; the Gallatin core is derived from the Pentium 4 "Northwood" design that powered the P4's successful run between 2GHz and 3GHz over the past couple of years. Newer P4s are based on the 90nm "Prescott" core, a substantially redesigned processor that offers higher performance in some cases and lower in others.

Intel today is launching a new version of the Pentium 4 Extreme Edition, and because it's not based on the Prescott core, it lacks certain new features, such as support for SSE3 instructions. What it does have, however, is one very important attribute: the ability to run on a 1066MHz bus. The new P4 Extreme Edition's partner in crime is the Intel 925XE Express chipset, a slightly tweaked version of the 925X Express chipset that also allows for a 1066MHz front-side bus, up from 800MHz. This faster bus should remove a key bottleneck, allowing the CPU to talk to dual channels of 533MHz DDR2 memory with the benefit of symmetry. (533MHz times two, you see, is 1066MHz. Clever, no?)

The big question about this new Extreme Edition processor is whether a faster bus alone can bring its performance into truly extreme territory. The new CPU runs at 3.46GHz, only up 66MHz from the 3.4GHz version that preceded it. Well, OK, 66.6666666666667MHz, to be exact. In our last CPU review, the Extreme Edition 3.4GHz was exposed like Ashlee Simpson on SNL. The regular ol' Pentium 4 560 at 3.6GHz—a product that costs less than half the price—often outperformed the Extreme Edition 3.4GHz, and AMD's range of Athlon 64 processors absolutely embarrassed the Pentium 4s in our gaming tests. Doom 3 was playing, but the P4's lips weren't moving. Can the Extreme Edition's massive cache, fast DDR2 memory, and a faster system bus restore some of the luster to Intel's flagship product? We're about to find out.

The new chip and set
The new P4 Extreme Edition comes in a pin-free package, ready to slide into a newfangled LGA775 CPU socket where the pins are on the motherboard. That makes the P4 Extreme Edition a fairly sturdy bit of hardware compared to most CPUs. Let's give it the extreme close-up treatment.



The P4 Extreme Edition 3.4GHz processor.

If you look closely at the picture, you can see the tiny indentations in the gold contact pads on the underside of the CPU where the pins of the LGA775 socket have made contact. Funky, huh? Having used LGA775 for a while now, I'm still not 100% sure about its sturdiness over the long haul, but my initial positive impressions remain largely confirmed. Handle it carefully, and the thing just works. Bust something, and in this case, you've gotta replace a $200 motherboard instead of a $1000 processor. Not a bad trade-off, all things considered.

The 925XE Express core logic chipset mated to the new Extreme Edition is just a tweaked version of the 925X Express, but that's no bad thing. Intel's 900-series chipsets are easily the most advanced core logic silicon available today, with support for a range of new technologies and standards, including PCI Express, DDR2 memory, Intel High Definition Audio, and advanced Serial ATA storage. If you're not already familiar with the 900-series Express chipsets, you owe it to yourself to go read our review of them. Intel has revamped large swaths of the PC platform with these chipsets. A number of companies are preparing core logic chipsets for the Athlon 64 that include support for PCI Express and some of the other new standards in the Intel 900 series, but it looks like none of them will support the full spectrum of new goodies like Intel. Also, those chipsets haven't quite arrived yet, so the Pentium 4 is currently your only choice for PCI Express.

A bus with only one seat?
One of the most surprising things about the new Extreme Edition processor is that it stands alone as the only Pentium 4 capable of running on a 1066MHz bus. This is a unique situation for Intel; in the past, the company has traditionally rolled out a new bus speed across most of its desktop processors in one stroke. Not so here.

I was puzzled by this decision, so I asked an Intel PR rep about the rationale behind it. He said the 1066MHz bus would not make its way to regular Prescott-based Pentium 4s, at least through the end of 2004, for three reasons. First, Intel wants the faster bus speed to be a product differentiator for the Extreme Edition CPU. Second, it takes time to ramp volume on new products with faster bus speeds. Third, Intel "can't just magically" make all CPUs work properly at a 1066MHz front-side bus.

I believe this is an example of the time-honored PR tradition of listing one's reasons in ascending order of importance. More likely than not, the 1066MHz bus will be confined to Extreme Edition processors because not all Prescott-based P4s are happy on a higher frequency bus. The fact that the Extreme Edition is still based on an older CPU core is telling. If Intel could roll out a 1066MHz bus across its entire Pentium 4 line without too much pain, I believe the company would do so sooner rather than later.

Whatever the case, the new Extreme Edition is the only P4 with official support for a 1066MHz bus, and the very nice Intel D925XECV2 mobo wouldn't oblige our attempts to run a Prescott CPU on a 1066MHz FSB. I expect the first wave of 925XE motherboards from Taiwan will be more obliging, opening up some interesting overclocking possibilities for lower-end P4 chips.

Anyhow, that's for another day. For now, let's see how the new Extreme Edition performs.