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X48 Motherboard Comparison

The X48 Northbridge: X38 Redux?

Few users question the notion that today's fastest systems will use Intel's highest-model PC chipsets, since these have consistently outpaced rival controllers in overclocking capability. Even builders who don't overclock can appreciate the added stability required for Intel to reach this position, but is the introduction of a new chipset model name a good enough reason to rush out and buy a new motherboard?

A brief look back to former chipsets shows that Intel's biggest breakthrough in high-speed stability dates to the P965 release of 2006. Though the P35 Express that replaced it was somewhat better, added features appeared to be the only reason for buyers to spend more for the upscale X38 Express that followed. Now Intel would like us to consider its latest "Ultimate Feature", official support for FSB-1600 processors via the X48 Express. But given that most X38 and many P35 motherboards can automatically configure FSB-1600 already, we can see where a few readers might not yet be convinced of the X48's necessity.

There's been much debate over the significance of Intel's X48 Express northbridge, with some arguing that its nothing more than an X38 validated at a higher clock speed, and others claiming that the additional validation makes these chips special. Some even compare the processor market, where the Core 2 Extreme QX6850 Compare Prices on QX6850 Processor and latest-production Core 2 Quad Q6600 use the same G0 stepping cores. Yet the QX6850 contains an added feature over the G0 stepping Q6600, as all Intel Extreme processors have the multipliers unlocked in both the upward and downward directions. Do X48 buyers benefit from such added features? Let's take a closer look.

At first, the X48 Express appears to have a reduced feature set compared to the X38, but the standard features are still there. Intel left a few of the basic functions out of this particular chart, to focus our attention on the X48 Express northbridge's performance-oriented features.

One recently-introduced feature we did notice is Intel XMP memory mode, but the technology isn't exclusive to the X48 Express - most motherboard manufacturers already advertise XMP support for previously-introduced X38 Express models. Like NVidia's "SLI Memory Mode" which is known among memory venders as "Enhanced Performance Profiles" (EPP), Intel's XMP technology adds semi-automatic overclocking profiles to memory's basic SPD values, which users may select from within the BIOS. Both technologies are meant to aid neophytes in reaching the rated speeds and timings of "factory overclocked" performance RAM, but XMP applies to DDR3, where EPP was for DDR2.

While the X48 Express officially adds FSB-1600 support, the needed 400 MHz bootstrap was also present in the X38 Express. Indeed, many motherboard manufacturers are now producing X48 models based on the same circuit boards as their X38 predecessors, leaving the possibility of higher bus speeds as the only reason to choose an X48 Express based board over an otherwise-identical X38 Express model. Some enterprising X38 platform owners may even try to use the corresponding X48 BIOS, though we wouldn't recommend it: if two boards really are identical except in name, the BIOS should also be identical except for its label. Any move by a company to withhold BIOS improvements from X38 models in order to boost X48 sales would be a cheap shot towards existing customers.

The boards might not differ much from their X38 forerunners, but that hasn't prevented Intel from charging motherboard producers a price premium for the additional validation. Though a few manufacturers saw the price difference as a good reason to ignore Intel's latest offering, others saw an opportunity to use the higher-validated X48 Express to highlight their products' high-speed capabilities. Four motherboards arrived at our lab in time for today's review.

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Thomas Soderstrom is a Senior Staff Editor at Tom's Hardware US. He tests and reviews cases, cooling, memory and motherboards.