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Intel's Skulltrail dual-socket enthusiast platform

Two sockets, eight cores, four PCIe slots—and one MHz increments

Skulltrail. If you hang around these parts, you've been hearing that codename bandied about for the better part of a year now. Not only does it have the distinction of being, quite probably, the single coolest codename known to all of geekdom, but it's also attached to the sort of hardware required to back up the copious bravado it implies. You see, Skulltrail is a high-end desktop PC platform based on workstation-class chips taken from Intel's Xeon parts shelf. We're talking about some wicked numbers here, such as dual sockets, eight cores, four graphics card slots, and dual 1600MHz front-side buses with a total of 25.6GB/s of bandwidth.


Of course, Xeon-based workstations have long sported impressive stats, but they've rarely set PC hobbyists' hearts aflutter for various reasons. Chief among them: buttoned-down motherboards with very little tweakability, foreign expansion options, and limited feature sets. We ran into these problems when we reviewed Intel's powerful-yet-frustrating V8 "media creation platform" last May. When your mobo's BIOS seemingly equates changing the CAS latency with opening up a liquor store in Riyadh, you know you're in the wrong neighborhood. Miraculously, though, some folks inside of Intel managed to wrangle approval to do something about that problem, and Skulltrail is the result: a truly tweakable motherboard coupled with unlocked Core 2 Extreme QX9775 processors clocked at 3.2GHz, primed for use with both SLI and CrossFire.

Beautimous, isn't it?

We probably have AMD to thank for Skulltrail's existence. When it couldn't keep up with Intel by delivering four cores per socket, the firm hatched its Quad FX scheme and pledged to make enthusiast-class dual-socket motherboards a part of its long-term technology direction. That direction was to include an upgrade to dual quad-core Phenom processors as soon as they became available. Of course, AMD has since canceled Quad FX and failed to provide the promised upgrade path for owners of Quad FX systems, but Skulltrail was already deep into development by the time AMD peed down its leg. End result: Intel makes good on its answer to AMD's promises. I can live with that.

The D5400XS motherboard

Indeed, Skulltrail is very easy to live with thanks to a motherboard expressly tailored for this purpose. The technology's workstation heritage is clear—it's based on the Stoakley platform and 45nm Harpertown Xeons we reviewed last fall—but the motherboard is utterly devoid of PCI-X slots and the like. Instead, the Intel D5400XS bristles with the sort of amenities a desktop rig might need. Here's a quick look at the key specs.

CPU support Dual LGA771-based Core 2 Extreme and Xeon processors
North bridge Intel 5400 MCH
South bridge Intel 6321ESB ICH
Interconnect PCIe x4 + DMI x4
Expansion slots 4 PCI Express x16 (PCIe 1.1) via dual Nvidia nForce 100 switches
2 32-bit PCI
Memory 4 240-pin FB-DIMM sockets
Maximum of 16GB of DDR2-667/800 FB-DIMM memory
Storage I/O 1 ATA/100 port
6 Serial ATA 3Gbps ports with RAID 0, 1, 5, 10 support
Audio 8-channel HD audio via 6321ESB and SigmaTel STAC9274D5 codec
Ports and Headers 2 eSATA with RAID 0,1 support via Marvell 88SE6121
USB 2.0 with headers for 4 more
1 RJ45 Ethernet 10/100/1000 via Intel 82573L
1 IEEE1394 (FireWire) with header for 1 more via TI TSB43AB22A

1 analog front out
1 analog center/LFE out
1 analog rear out
1 analog surround out/line in
1 analog mic in
1 TOS-Link digital S/PDIF out

1 HD Audio front-panel header for analog headphone out and mic in
1 HD Audio Link header
1 3-pin S/PDIF out header

1 Consumer Infrared front-panel receiver header
1 Consumer Infrared transmitter header

Form factor EATX (13" x 12") with LGA775-style mounting holes for cooling

In a nutshell, this thing is loaded. Intel has backed up the specs with additional goodness where possible, too. For instance, the D5400XS's eight-channel audio is Dolby Home Theater capable, which means it supports both Pro Logic II and Dolby Digital Live encoding.

In some ways, of course, the D5400XS's workstation-class foundation is inescapable, but Intel has made accommodations where possible. Although it uses Xeon-style LGA771 processor sockets, the mounting holes around those sockets use LGA775-style spacing, so they should be compatible with desktop-class coolers, including the more exotic varieties involving liquid cooling or phase-change. Similarly, cramming all of the D5400XS's features onto a standard ATX-sized board would be nearly impossible, but the 13" x 12" board is small enough to fit into an EATX-ready enclosure like the Cooler Master Cosmos.

One place where Skulltrail can't escape its workstation heritage is in its use of fully buffered DIMMs. FB-DIMMs are typically more expensive than standard DDR2 memory, and they consume more power than standard DIMMs. FB-DIMMs also tend to have higher latency than DDR2 memory. They somewhat make up for these drawbacks in server and workstation settings by allowing tremendous amounts of bandwidth and lots and lots of DIMM slots with fewer traces on the motherboard.

The D5400XS has only four FB-DIMM slots, but each one of those slots is connected to a memory channel in the Intel 5400 north bridge. This north bridge has two separate memory "branches" with two channels each. Fully populated with 800MHz memory modules, this board can sustain a peak throughput of 25.6GB/s to main memory—enough to saturate its dual 1600MHz front-side buses. Our Skulltrail sample came from Intel with a pair of 800MHz FB-DIMMs, and that's how we tested it. Adding two more memory modules would have increased the system's peak bandwidth, but at the cost of additional memory access latency and power consumption.