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Intel's X48 Express chipset


1600MHz front-side bus or bust
— 12:56 PM on March 14, 2008

Intel's Core 2 Extreme QX9770 is due out this quarter, bringing with it not only four Penryn cores clocked at 3.2GHz, but also a front-side bus running at 1600MHz. That faster FSB presents a bit of a problem, though, because Intel's current P35 and X38 Express chipsets only support front-side bus speeds up to 1333MHz. So the QX9770 needs a new chipset, or at least a new north bridge, which is where the X48 Express comes in.

Based on Intel's existing X38 Express, the X48 brings with it official support for 1600MHz front-side bus speeds. With this faster bus, the X48 looks poised to supplant its predecessor atop Intel's chipset lineup, which means a new wave of motherboards is coming from all the usual suspects.

Gigabyte's X48T-DQ6 is the first X48 offering to hit our labs, and in addition to packing Intel's latest chipset, it comes with an innovative Dynamic Energy Saver mechanism designed to lower power consumption. Join us as we put this power saving scheme to the test and run the X48 Express through it paces against the rest of Intel's chipset lineup.


A new north bridge
The X48 Express' defining feature is its new north bridge component—a chip that might not actually be new at all. Intel engages in a process called binning with its processors, sorting what are essentially identical chips based on the clock speeds at which they're comfortable running. The same approach could be applied to north bridge chips, making the X48 a bin sort of X38 chips comfortable running a 1600MHz front-side bus. Based on our own experiences overclocking a couple of X38 boards to front-side bus speeds of 2000MHz and higher, we'd wager there are plenty of X38 chips up to the task of a mere 1600MHz.

X48 Express X38 Express P35 Express
Front-side bus 1600/1333/1066MHz 1333/1066MHz 1333/1066MHz
Memory controller DDR2-800
DDR3-1600
DDR2-800
DDR3-1333
DDR2-800
DDR3-1066
PCI Express 1.1 lanes 0 0 16
PCI Express 2.0 lanes 32 32 0
Multi-GPU support CrossFire CrossFire CrossFire*
Chipset interconnect DMI DMI DMI
Peak interconnect bandwidth 2GB/s 2GB/s 2GB/s

Apart from its faster system bus, the X48's features mirror those of the X38 Express. Both feature 32 second-generation PCI Express lanes, providing substantial bandwidth to not only single graphics cards, but also CrossFire configurations. However, despite working with Nvidia to bring SLI support to its Skulltrail platform, Intel's desktop chipsets remain locked out of the green team's multi-GPU rendering scheme. That strikes us as particularly petty on Nvidia's part, and while it blunts some of the X48's appeal, CrossFire has matured into a viable and in some cases preferable alternative to SLI.


The X48 Express north bridge chip cap
Falling prices have kept DDR2 memory popular among enthusiasts, so it's a good thing the X48 retains support for the older memory type. Expect the first X48 boards to have DDR3 memory slots, though. Based on our conversations with motherboard makers, it looks like most are aiming for DDR3 first, with DDR2 offerings to follow.

On the DDR3 front, the X48 should support memory bus speeds up to 1600MHz. However, depending on your motherboard, that top memory speed may only be available if you're also running a 1600MHz front-side bus. Our Gigabyte X48T-DQ6 lacks the dividers necessary to run 1600MHz memory with a 1333MHz FSB, for example, and others are also likely to face this limitation. Motherboard makers have some leeway when it comes to defining bus dividers, which is why you'll find plenty of P35 Express boards capable of clocking DDR3 memory at 1333MHz, despite the fact that the chipset only officially supports memory bus speeds up to 1066MHz.


Hardly a secret, the ICH9R shows up at the south bridge
While it's unclear whether the X48 north bridge chip is merely a carefully selected and further validated X38, the chipset's south bridge component is Intel's existing ICH9R. Don't let the "Secret" chip marking fool you; this is the same silicon Intel launched last summer with the P35 Express. Nearly a year after its initial launch, the ICH9R still packs a competitive feature set, including six SATA RAID ports, 12 USB ports, and six gen-one PCI Express lanes. Intel also says the ICH9R has an embedded Gigabit Ethernet controller, although we've yet to see a motherboard actually make use of it.

DDR3 rises to the occasion
Intel first cracked the seal on DDR3 memory with its P35 Express chipset, and at the time, the new memory type hardly looked poised to take over from DDR2. Prices were too high, for one, and DDR3 hadn't yet ramped to significantly higher clock speeds than existing DDR2 modules. But times have changed, speeds have scaled, and prices have fallen.


Today, DDR3 memory is available at speeds as high as 2000MHz. That's an impressive milestone considering that DDR3 started out at roughly half that speed nearly a year ago. Those of us who have been around for a while will remember that DDR2 certainly didn't ramp this quickly after its initial launch.

Unfortunately, there's still an inescapable price premium associated with DDR3. Modules like Corsair's CM3X1024-1600C7DHX, which are rated for 7-7-7-20 timings at 1600MHz, run about $400 for a 2GB dual-channel kit. Believe it or not that's an improvement over what was available last summer, when $400 would have only bought you a 2GB kit of DDR3-1066 memory rated for 9-9-9-24 timings. The price of 2GB DDR3-1066 kits has fallen to around $220.

Despite falling DDR3 prices, the fact that the bottom has essentially dropped out of the DDR2 memory market makes for a tough sell. DDR3 is undoubtedly the future, but when you can get 2GB of DDR2 for less than $50, paying more than four times the price for DDR3 is difficult—if not impossible—to justify rationally.