Intel Skulltrail

Once upon a time there was a CPU called Xeon. Despite being incredibly fast, this CPU was locked inside a giant white case, tucked away in the corner of a server room and rarely allowed outside to play. Despite the occasional overclockable dual CPU motherboard, such as the legendary Asus PC-DL Deluxe (see Issue 2, p43), Xeon remained firmly in the realm of the super-rich enthusiast and the businessman.

However, just in time for Xeon’s tenth birthday (this June), Intel has finally decided to produce what enthusiasts have long been asking for: an overclockable Xeon platform. The end result is known as Skulltrail, one of the silliest, most testosterone-fuelled marketing names the industry has produced. Skulltrail is a combination of an Intel D5400XS motherboard and a pair of LGA771 quad-core Xeons that have been tweaked and rebranded as Core 2 Extreme QX9775s.

Although Skulltrail is clearly based on Xeon technology, it differs in a number of key areas. The changes are subtle, though, so you could be forgiven for confusing a pair of Core 2 Extreme QX9775s with a pair of Xeon X5482s. After all, both CPUs fit the server-and-workstation LGA771 socket rather than the usual LGA775 (the two aren’t compatible), and share the same specs. The QX9775 and X5482 both have four cores running at 3.2GHz, 12MB of Level 2 cache (6MB per pair of cores) and a 400MHz (1,600MHz effective) FSB. However, while the four pre-fetchers inside an X5482 are optimised for running workstation/server applications such as CAD, 3D rendering and databases, the pre-fetchers in the QX9775 are tuned for desktop applications and games. In addition, the QX9775 justifies its Core 2 Extreme branding by having an unlocked multiplier, making it more amenable to overclocking. Both the Core 2 Extreme QX9775 and Xeon X5482 are based on the awesome 45nm Penryn architecture, so they’re very power-efficient.

The other half of the Skulltrail platform is the Intel D5400XS motherboard. This E-ATX monster is based on the same Intel 5400 chipset found on new Xeon motherboards such as the SuperMicro X7DAW-N (see Issue 53, p44). Unfortunately, this means that you’re forced to use expensive (and relatively slow) 800MHz PC2-6400 FBDIMMs, instead of standard DDR2 or DDR3.

The most obvious example of the D5400XS’s enthusiast leanings is its incredible number of high-speed expansion slots. There are four 16x PCI-E 1.1 slots and two PCI slots but, oddly, not all of these are fed by the Northbridge and Southbridge. Plus, doesn’t the 5400 chipset support PCI-E 2.0? Indeed it does, but Intel has fitted the four graphics slots of the D5400XS with two Nvidia nForce 100 chips. These are the chips that Nvidia uses to make SLI work. This is a huge deal, as Nvidia didn’t previously sell nForce 100 chips to other manufacturers, thereby ensuring that you had to buy a high-end nForce SLI motherboard if you wanted SLI graphics. As with most current Intel chipsets, the 5400 also supports CrossFire.

One of the best aspects of the D5400XS is that, although the CPUs are LGA771, the PCB has been designed so that you can use LGA775 coolers. You therefore have much more freedom to use a funky cooler, rather than having to choose from the limited range of LGA771 coolers. Sticking with the cooling theme, each CPU socket has its own VRM circuit, with each MOSFET cooled by a giant heatsink. What’s more, even when running heavily overclocked and overvolted, the VRM heatsinks never become particularly hot. However, you’ll need to position fans to blow over the hot-running FBDIMMs and Northbridge.

Although Intel has designed enthusiast motherboards before, we haven’t seen one to rival the best boards from Abit, Asus and DFI. However, it’s clear that a lot more work has gone into the D5400XS. The board is bristling with useful extras, such as power and reset buttons, and there are eight temperature probes scattered around. The PCB even has four LEDs that indicate if a CPU or its VRM circuit is beginning to overheat. There’s also a two-digit POST code display, which can identify errors if the system isn’t POSTing properly. The BIOS can also adjust the speed of the fan cooling the Southbridge and nForce 100 chips, although you can also use a standard 3-pin rheostat.

On the more mundane front, the D5400XS has six RAID-capable S-ATA II ports, plus a pair of eSATA ports. There’s a cluster of ten USB 2 ports, a pair of FireWire ports and even a single EIDE port in case, for some strange reason, you haven’t bought a S-ATA optical drive yet. There’s also 8-channel Intel HD Audio, although we suspect that most hardcore gamers would fill one of the PCI slots with a dedicated sound card.

PERFORMANCE

Out of the box, our Skulltrail system turned in almost identical performance numbers as the SuperMicro X7DWA-N system that we tested in Issue 53. This is what you’d expect, as both motherboards are based on the 5400 chipset, and have a pair of quad-core 3.2GHz Penryn CPUs and 800MHz PC2-6400 FBDIMM memory.

Ultimately though, with no BIOS tweaks available, the SuperMicro Xeon system could never hope to improve on its overall Media Benchmark score of 1,451. In contrast, the BIOS of the D5400XS provides the option to increase the CPU multiplier and boost the FSB from 400MHz to 550MHz. There’s also a good range of voltage options, including the ability to shoot up to 1.9V through each CPU (which can be adjusted independently of each other). Other voltage treats include Northbridge, FSB and GTL (Gunning Transceiver Logic, which will help with system stability if the dual-core dies in a single quad-core CPU package are slightly mismatched). You can also adjust the voltage of the AMB control chip on each FBDIMM, along with the voltage of the DRAM chips themselves.

Another impressive aspect of the D5400XS is the high-quality VRMs. On most motherboards, the vcore will droop (known in the trade as vdroop) when the CPU is under load, but on the D5400XS, the vcore barely drooped at all, even when we overvolted and overclocked the CPUs. This is a big deal, as vdroop is one of the biggest causes of instability when overclocking.

Of this array of options and voltage controls, the most important are the voltage options of the Northbridge, FSB and CPU; even when overvolted, we could barely overclock the RAM. After several BIOS updates, and several days of experimentation, we found that the D5400XS refused to run stably with the FSB set any higher than 420MHz (1,680MHz effective), a tiny increase of only 20MHz. This is very disappointing, but after raising the CPU multiplier from 8 to 10, we succeeded in overclocking the two QX9775s from 3.2GHz to 4.2GHz. We needed to raise the vcore from 1.25V to 1.525V, the Northbridge from 1.25V to 1.55V and the FSB from 1.2V to 1.5V to keep this overclock stable.

This is around the same level of overclock as you’d expect a Core 2 Extreme QX9650 or QX9770 to achieve with air cooling. For it to go any further you’d need to invest in water cooling, phase change or LN2. At 4.2GHz, our Skulltrail system achieved an overall score of 1,854, making this one of the fastest air-cooled PCs in the world.

Click here to see the benchmarks (opens in a new window).

CONCLUSION

Many enthusiasts have been waiting a long time for Intel and Nvidia to resolve their differences, and release a motherboard based on an Intel chipset that supports SLI. However, others have waited longer for Intel to release an easily overclockable dual-processor motherboard.

For these people, Skulltrail is a dream come true. Thanks to the presence of the nForce 100 chips, the D5400XS runs two graphics cards in SLI like a charm and offers the potential of having an octo-core system running at over 4GHz. A Skulltrail system won’t be cheap, but the D5400XS supports standard LGA771 Xeons, so you could save money by buying a pair of cheaper Xeons instead, although they’d be less overclockable than a pair of Core 2 Extreme QX9775s.

INTEL D5400XS IN DETAIL

Chipset Intel 5400

CPU support LGA771 Xeon 5100/5300/5400-series, LGA771 Core 2 Extreme

Memory support 4 slots: max 16GB FBDIMM DDR2 (PC2-6400)

Expansion slots Four 16x PCI-E slots (PCI-E 1.1), two PCI slots

Sound Intel HD Audio via IDT STAC9274 with 8-channel support

Networking Gigabit Ethernet

Overclocking CPU clock 133 - 550MHz; max voltages, CPU 1.9V, AMB DDR2 2.5V, DRAM DDR2 2.8V, Northbridge 1.6V, FSB 1.5V

Ports 6 x S-ATA II, 2 x eSATA II, EIDE, floppy, 10 x USB 2, LAN, 4 x surround audio out, line in, mic, 2 x FireWire

Dimensions (mm) 330 x 305

INTEL CORE 2 EXTREME QX9775 IN DETAIL

Frequency 3.2GHz

Core Harpertown

Number of cores 4 x physical

FSB 400MHz (1,600MHz effective)

Level 1 cache 32KB + 32KB (each core)

Level 2 cache 2 x 6MB (shared)

Packaging LGA771

Thermal Design Power (TDP) 150W

Features SSE3, SSE4, EM64T, EIST, Execute Disable Bit, SMP (up to two CPUs)

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Asus Striker II Formula	59%
MSI P7N SLI Platinum	74%
Gigabyte GA-X48-DQ6	74%
XFX MB-N780-ISH9	72%
Intel Skulltrail	90%
Asus P5E3 Premium WiFi-AP	77%

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