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Sandy Bridge-E motherboards from Asus, Gigabyte, Intel, and MSI

The X79 Express cometh

Intel is in a unique position in the market for ultra-high-end desktop PCs: it essentially has no competition. AMD hasn't priced a desktop processor far north of $300 in years, while Intel has been selling six-core Gulftown CPUs at up to a grand a pop. With no one nipping at its heels, Intel has had the luxury of updating its flagship platform at what could charitably be described as a conservative pace.

When Gulftown made its debut with the Core i7-980X Extreme in early 2010, it breathed new life into an X58 Express platform that had been around since 2008. Only 133MHz has been added to Gulftown's top end since, and the X58 hasn't been touched, save for motherboard makers rolling out new models that augment the chipset with next-gen peripherals. So, yeah, Sandy Bridge-E and its accompanying X79 Express chipset have been a long time coming.

The two are inseparable thanks to a new LGA2011 socket with a rather timely pin count. If you want to get in on a six-core Sandy Bridge CPU, you're gonna need a new motherboard. But which one? That's a daunting question given the complexity of modern mobo designs, which house ever-growing peripheral payloads in addition to rapidly evolving firmware. To help make sense of your options, we've rounded up four LGA2011 boards from the biggest players in the business. Join us as the Asus P8X79 PRO, Gigabyte X79-UD5, Intel DX79SI, and MSI X79A-GD65 (8D) square off to see which is the best foundation for Sandy Bridge-E.

E is for Enterprise Extreme
If you haven't already read Scott's in-depth look at the Core i7-3960X, I recommend it as a starting point. This round-up will focus primarily on how the different motherboards compare rather than looking too deeply into the intricacies of the processor. We should, however, pause for a moment to drink in the glorious excess that is Sandy Bridge-E. Intel's new flagship has a six-pack of Sandy Bridge cores backed by up to 15MB of last-level cache—50% more cores and nearly double the cache of the Core i7-2700K.

Sandy Bridge-E doesn't have more cores than Gulftown (if you don't count the additional two cores that Intel has chosen to disable for desktop-bound versions of the silicon), but it does increase the number of memory channels from three to four. Intel officially supports 1600MHz memory with one DIMM per channel, an increase from 1333MHz in both Gulftown and the Sandy Bridge CPUs that plug into LGA1155 sockets. Motherboard makers say their boards can handle higher memory speeds when paired with suitably fancy DIMMs, of course.

While Intel's last halo platform consolidated much of its PCI Express connectivity in a north-bridge chip, Sandy Bridge-E has PCIe lanes built into the CPU. This is the first implementation we've seen of PCI Express 3.0, although Intel is very precise about how it talks about such things. The platform's official block diagram lists PCI Express 2.0 lanes attached to the CPU, but buried in the technical documentation is an assertion that the PCIe connectivity is "fully-compliant to the PCI Express* Base Specification, Revision 3.0." Third-gen PCI Express devices simply don't exist in the wild, and Intel won't be confident about compatibility until it has hardware to verify. Presumably, hardware that is likewise compliant with the spec will work at PCIe 3.0 speeds.

Source: Intel

Extra speed isn't the only perk to gen-three PCI Express, but it's one of the biggest benefits. Each lane has an 8GT/s data rate, up from 5GT/s with PCIe 2.0. The data is processed differently with the new spec, which scrambles the bits using binary math before feeding them through a 128b/130b encoding scheme whose overhead is an order of magnitude smaller than with the 8b/10b encoding from the old standard. As a result, PCIe 3.0 squeezes 1GB/s of bidirectional bandwidth out of its 8GT/s, doubling the effective throughput of gen-two PCIe with only a 60% increase in the data rate.

There are 40 PCIe 3.0 lanes in CPU split between three links: two with 16 lanes each and one with eight. One of the x16s can be split into a pair of x8s for four-way graphics goodness in an x16/x8/x8/x8 config. If you don't need quite as much bandwidth per lane, one of the x8s can be cleaved into a pair of x4s. It would take a very fast PCIe SSD to saturate a fraction of the bandwidth available in just one of those quad-lane links.

Even more PCI Express lanes are housed within the Sandy Bridge-E die, but they hail from the second generation and have been repurposed as a chipset interconnect. A four-lane DMI link connects the CPU to its X79 Express sidekick, providing 2GB/s of bandwidth in each direction.

The X79 was supposed to have a second interconnect dedicated to new storage-controller logic bristling with 6Gbps SATA and Serial Attached SCSI ports. Dubbed SCU, this controller would have been a nice bit of baggage from Sandy Bridge-E's real mission in enterprise environments. Unfortunately, the SCU and its associated interconnect have been "de-featured" on the chip "as a result of silicon health." Intel wanted to meet its November 2011 launch schedule for the platform (cosmic alignment, perhaps?), and it apparently couldn't get the SCU working in time.

We started hearing rumors about issues with the X79's new storage hotness late this summer, and that might explain why the platform didn't launch in the August/September timeframe expected by all the motherboard makers we spoke with at Computex in June. Intel suffered an embarrassing SATA bug that forced the recall of its initial Sandy Bridge chipsets earlier this year; perhaps it was contagious.

The X79 Express platform hub

With the SCU and its accompanying interconnect fused shut, the X79 looks a lot like Intel's existing P67 platform hub. Note that I didn't say Z68, which offers QuickSync video transcoding and Smart Response SSD caching. Sandy Bridge-E lacks an integrated GPU, so it can't play the QuickSync game, and Intel hasn't finished porting Smart Response to the platform. We're told SSD caching will be integrated into a driver update due midway through next year, which seems like an awfully long time to wait given the fact that the X79 has similar storage controller logic to the Z68.

Like the bulk of Intel's 6-series lineup, the X79 has dual SATA controllers: one with two 6Gbps ports, and another with four 3Gbps ones. RAID is on the menu, of course, but the array of SATA ports isn't particularly aspirational considering the fact that AMD serves up six 6Gbps ports in its chipsets. Then again, high-performance SSDs are migrating toward PCI Express, which Sandy Bridge-E has in spades.

Speaking of PCIe, there are eight second-generation lanes in the X79 reserved for expansion slots and peripherals—like extra 6Gbps SATA controllers. As with the SATA ports, the logic is similar to what's in Intel's other desktop chipsets. The same goes for the Gigabit Ethernet and USB 2.0 controllers. USB 3.0 would've been a nice inclusion, but given Intel's enterprise focus for Sandy Bridge-E, I can understand why more SATA and SAS ports took priority. If only they had worked.

Cutting-edge 32-nm process technology is used to create Sandy Bridge-E silicon, while Intel uses its 65-nm fab capacity to crank out the X79. Interestingly, the chip's 7.8W TDP is higher than the 6.1W rating for the P67, which has essentially the same feature set. I suspect the extra transistors associated with supporting the SCU are responsible for that discrepancy.

The X79 Express four ways
Every time a new platform launches, I tell myself to be less ambitious with the initial motherboard round-up. And every time, I fail. We've rounded up no fewer than four motherboards to see what Asus, Gigabyte, Intel, and MSI have concocted for Sandy Bridge-E.

Asus P9X79 PRO Intel DX79SI Gigabyte X79-UD5 MSI X79A-GD65 (8D)
DIMM slots 8 DDR3 8 DDR3 8 DDR3 8 DDR3
Expansion slots 2 PCIe 3.0 x16
2 PCIe 3.0 x16 (x8)
2 PCIe 2.0 x1
2 PCIe 3.0 x16
1 PCIe 3.0 x16 (x8)
2 PCIe 2.0 x1
2 PCIe 3.0 x16
1 PCIe 3.0 x16 (x8)
2 PCIe 2.0 x1
2 PCIe 3.0 x16
1 PCIe 3.0 x16 (x8)
2 PCIe 2.0 x16 (x1)
1 PCIe 2.0 x1
Gigabit Ethernet Intel 82579V Intel 82574L
Intel 82579LM
Intel 82579 Intel 82579
USB 3.0 2 x ASMedia ASM1042
2 x NEC D720200 2 x Fresco FL1009 2 x NEC D720200
Auxiliary SATA ASMedia ASM1061
Marvell 88SE9128
NA 3 x Marvell 88SE9172 ASMedia ASM1061
Audio Realtek ALC898 Realtek ALC892 Realtek ALC898 Realtek ALC892
FireWire NA VIA VT6315N VIA VT6308 VIA VT6315N
Warranty Three years Three years Three years Three years
Price $329 $280-300 $350 $280-299

All of the boards have eight DIMM slots and at least three PCI Express x16 slots. Their expansion slot configurations are otherwise quite different, although there is agreement on the Ethernet front. Motherboard makers are finally using the Gigabit Ethernet MAC included in the chipset rather than farming out networking to discrete Realtek controllers.

Since there's no USB 3.0 connectivity in the chipset, mobo makers must employ auxiliary controllers. All but the Intel board is equipped with additional SATA connectivity, as well. I guess slapping a couple of additional 6Gbps ports onto the DX79SI would've been an admission that the two in the chipset aren't enough.

The Asus board is the only one among the four to cut the cord on FireWire. That's somewhat disappointing in light of the fact that the P9X79 PRO is among the most expensive of the lot. At least the board features Realtek's latest ALC898 audio codec, which also appears on Gigabyte's X79-UD5. Distilling these boards down to their base specifications doesn't do them justice, though. Let's take a closer look at what each one brings to the table.