Kinky Luxury: Intel Skulltrail Platform Review

$3000 for two quad-core processors from Penryn family, $650 for a special mainboard and $200 for memory: this is a new exclusive dual-processor platform for enthusiasts from Intel. However, do investments like that really make sense for the sake of unattainable performance?

by Ilya Gavrichenkov
02/22/2008 | 05:29 PM

Aggressive promotion of multi-core ideology has evidently stimulated increased interest in dual-processor desktop systems on the users’ as well as on the manufacturers’ part. The thing is that the launch of dual-core and quad-core processors pushes software developers to start paying more attention to optimizing their products for multi-threaded environments. As a result, many contemporary applications that require significant resources benefit a lot from running on CPUs with multiple cores.


Theoretically, this tendency opens doors to additional improvement of desktop systems performance that can be achieved by installing not juts one but two (or even more) multi-core processors in each of them. And although dual-socket processor systems are relatively complex and expensive to build and maintain, they can really boast unprecedented performance in a number of applications. These home users who are ready to forget about high price and operating expenses for the sake of hard-edged computational power are the main target group for the leading computer platform developers creating dual-processor systems made of the highest performing components. Today we are going to talk about one more platform like that offered by Intel Corporation. This system is known as Skulltrail and very soon it will be available in stores for the wealthiest and most dedicated computer enthusiasts.

I have to say that Intel is far not the first manufacturer to introduce and promote dual-processor desktop systems into the market. For example, in the far away 1999 ABIT offered computer enthusiasts their famous BP6 mainboard designed to support two Socket370 Celeron processors. And that was definitely not the only example. A year later VIA launched a special revision of their Apollo Pro133 core logic set intended specifically for dual-processor Socket370 systems. Dual-socket mainboards based on this chipset used to be pretty popular among computer enthusiasts even though there were very few applications that could really take advantage of the two processors.

AMD initiated the next wave of public interest towards dual-processor systems by offering their Quad FX platform over a year ago. This platform used a pair of dual-core Athlon 64 FX processors. During the platform launch AMD stressed the fact that this way they were setting new standards for high-performance desktop systems, however, in reality Quad FX was non other but a not very successful attempt to respond to Intel’s quad-core processors. Therefore, the life span of this platform was relatively short and later on AMD decided to give it up.

Nevertheless, Intel caught on to the idea of launching a non-server dual-socket platform. Last year we have already introduced to you the first concept of a platform like that known as Intel V8. Looked like Intel’s marketing specialists felt some excitement about solutions like that that is why the company continued research and development in this direction. It took Intel a few months to finalize and polish off this platform so that it could finally go into mass production. And today we are welcoming the result of this long work in progress, which is ready to go mass – Intel Skulltrail platform.

Although Intel Skulltrail including two quad-core Penryn processors has no analogues or competitors these days, it is extremely interesting to check out. Let’s see how good this monstrous system actually is and how valuable it is going to be from a practical standpoint. Our today’ article will try to answer the following question: can Intel Skulltrail become a really useful platform or it is interesting only as a vivid example of Intel’s financial power.

Closer Look at Intel Skulltrail

Core 2 Extreme QX9775 Processors

Just like the previous prototype, Intel Skulltrail platform has very evident server roots. And in fact, this is not surprising at all. Classical desktop Core 2 Quad processors from Yorkfield family cannot work in SMP configurations; the LGA775 socket is not designed for that also. That is why Skulltrail uses special processors that are more like the new Intel Xeon CPUs from Penryn family. They formally belong to Core 2 Extreme clan but are designed in typical server form-factor: LGA771.

Intel Skulltrail platform uses two Core 2 Extreme QX9775 processors with almost the same characteristics as those of the Core 2 Extreme QX9770 CPUs for standard LGA775 desktop platforms. In other words, Core 2 Extreme QX9775 is a combination of two dual-core dies manufactured with 45nm process and equipped with 6MB L2 cache memory that are stuck together into a single packaging. The nominal clock speed of Core 2 Extreme QX9775 processors is 3.2GHz and the bus works at 1600MHz.

The complete list of Core 2 Extreme QX9775 specifications is given in the table below:


Core 2 Extreme QX9775



Nominal frequency


Bus frequency




L2 cache

2 x 6MB





Production process








Enhanced Intel Speedstep


Intel 64


Intel Virtualization Technology


SIMD instructions support



2 x 410 mln.

Die size

2 x 107

Official price


There is nothing unexpected about these specifications. The only thing that catches your eye is probably the high TDP of 150W. However, in reality Core 2 Extreme QX9775 processors from the 45nm Penryn family do not really heat as greatly as you may have thought after checking out this spec sheet.

If we disregard the fact that Intel is trying hard to pass Core 2 Extreme QX9775 for a desktop solution, we will see evident relative connection between this CPU and Xeon X5482. In fact, the only thing that is different between them is the name.

CPU-Z diagnostic utility recognizes Core 2 Extreme QX9775 processor as Yorkfield, although we believe it would be more correct to give it a server name: Harpertown.

Although Skulltrail platform uses LGA771 processors, Core 2 Extreme QX9775 looks practically identical to CPUs for regular desktop LGA775 platforms.

Left - Core 2 extreme QX9775; right – Core 2 Extreme QX9770

However, you shouldn’t think that LGA771 and LGA775 are compatible: Intel made sure that you cannot install the CPU into the wrong socket by shifting the openings in the CPU base.

Left - Core 2 extreme QX9775; right – Core 2 Extreme QX9770

Intel D5400XS Desktop Board

As we see, Intel didn’t have to develop new processors for the Skulltrail platform. In fact, all the engineering work got down to putting new marking on the already existing Xeon X5482 CPUs. However, the same couldn’t be done for the mainboard that had to become the basis for the high-performance dual-socket desktop platform. I doubt hardware enthusiasts would like a server or workstation mainboard, they usually value different platform qualities.

Intel has already faced this problem when they introduced their V8 platform to the users. That system included a regular workstation board that didn’t really make the desired impression on the users, frankly speaking. Therefore, Intel learned its lesson and didn’t repeat the same mistake when working on the Skulltrail platform. The engineers had to design a specially adapted mainboard that was called Intel D5400XS Desktop Board.

However, it is important to understand that they didn’t have much room for creativity. Contemporary desktop chipsets targeted for top of the line systems do not support dual-socket configurations. That is why D5400XS was built on core logic set for servers and workstations called i5400B Express (codenamed Seaburg). This is today’s top Intel chipset supporting dual-socket systems working with 1600MHz bus. So, no wonder that Intel D5400XS Desktop Board supports not only Core 2 Extreme QX9775 processors, but is also compatible with the entire Xeon processor family targeted for dual-socket platforms. Taking into account that Core 2 Extreme QX9775 costs around $1500, it may be a very useful additional feature for the board.

Although i5400B Express chipset wasn’t initially designed for Skulltrail systems, is a very advanced solution in terms of supported features and functionality. In particular, one of its strengths is two independent processor busses with point-to-point topology serving to connect two CPUs within the same system. So, this chipset eliminates the bottleneck of previous-generation multi-processor systems on Xeon CPUs where all processors sat on the same bus.

Moreover, i5400B Express boasts one more feature that allows increasing the efficiency of communication between the CPUs and the memory. It features a special buffer called Snoop Filter containing the info on the location and urgency of all data used by the processors. Since MESI protocol used to maintain caches coherency in Xeon based multi-processor systems requires each of the CPUs to follow the processor bus of the other one, Snoop Filter allows reducing parasite traffic along processor busses significantly.

Two FSB busses and Snoop Filter are certainly a good thing for every dual-socket system, such as Skulltrail. But not all the i5400B Express features are equally advantageous for this platform. Server roots of the i5400B Express that are absolutely redundant for Skulltrail surface in the memory subsystem. They are the reason why D5400XS mainboard requires exotic for desktop systems FB-DIMM DDR2 memory modules. These modules look really nice in servers and workstations but in desktops are somewhat weird, I have to say. Their major feature is serial data transfer interface instead of the classical parallel one and it can really be beneficial if there are a lot of large capacity modules installed into the system at the same time. This is an absolutely useless feature for Skulltrail, especially since D5400XS mainboard has only four DIMM slots.

But we have no choice: potential Skulltrail owners will have to put up with all the disadvantages of using FB-DIMM such as slow speed and high power consumption and heat dissipation. According to our tests, even a four-channel memory controller of the i5400B Express chipset doesn’t help here: regular dual-channel DDR2 SDRAM works much faster, not to mention a much more up-to-date DDR3 SDRAM. Moreover, to achieve maximum performance on a Skulltrail platform you need to have four memory modules, i.e. all available memory slots need to be occupied.

However, we should give Intel engineers due credit: they did their best to make Intel D5400XS Desktop Board look as close to an enthusiast mainboard as possible, despite not the best chipset choice. For example, this mainboard features four PCI Express x16 slots. And even though i5400B Express chipset features 32 PCI Express lanes that can be split into 4 PCI Express x8 busses, the developers introduced a different and way more interesting implementation.

Available lanes are split between two PCI Express x16 busses with an Nvidia nForce 100 SLI bridge connected to each of them. This chip dynamically distributes the bandwidth of one PCI Express x16 bus between the two. Here I would also like to add that although i5400B Express supports new version of PCI Express specification, all graphics busses on D5400XS work only in PCI Express 1.1 mode, which is determined by the peculiarities of nForce 100 SLI chips.


It is also important that Intel engineers managed to avoid formal problems with SLI support thanks to Nvidia chips used on their D5400XS Desktop Board. That is why this mainboard became the first product on a third-party chipset that actually supports Nvidia SLI without any driver modifications. Of course, there are no problems with CrossFire support, too. In other words, D5400XS can work with almost any configurations with several graphics cards, which is an indisputable advantage of this product.

However, it turned out that Intel D5400XS doesn’t in fact support triple- and quad-SLI because of the notorious driver limitations. Nvidia drivers only allow SLI mode for those two graphics cards that are installed into the slots powered by the same nForce 100 SLI chip.

Another step towards computer enthusiasts was the introduction of the new cooler retention mechanism on Intel D5400XS. Luckily for hardcore users, the retention holes in the mainboard PCB are compatible with LGA775 cooling solutions and do not require server LGA771 cooling systems. It allows using Skulltrail platform with numerous efficient cooling solutions including not only the air coolers, but also liquid-cooling systems.

Intel D5400XS also has a few other features that make it look like a real overclocker platform. You can see that it has popular Power and Reset buttons as well as a POST-indicator.

At the same time, we have to point out a few frustrating drawbacks that may make potential Skulltrail owners pretty unhappy. Namely, it is the cooling of the key mainboard components: chipset North and South Bridges and the PCI Express bus bridges. There is a relatively big and low aluminum heatsink covering the South Bridge together with two Nvidia micro-chips. In the center of this heatsink there is a high-speed fan, 40mm in diameter. And although this whole thing provides pretty decent cooling for the chips, it is annoyingly loud, unfortunately. As for the chipset North Bridge cooling, it is topped with a passive aluminum heatsink with pretty tall ribbing. They recommend installing a fan on top of it, but it is missing from the bundle for some reason.

This chipset cooling solution is hardly acceptable for the top-of-the-line solutions. Mainboard makers have learned long ago to design very efficient passive cooling solutions with heatpipes, so we couldn’t really grasp why Intel didn’t do something like that.

The chipset South Bridge of Intel D5400XS is Intel 6321ESB chip. It is responsible for two PCI slots, nine USB 2.0 ports, six Serial ATA and one Parallel ATA ports.

Besides, the mainboard also features a number of integrated onboard controllers that provide gigabit network, Firewire interface, eSATA interface and integrated sound. on the mainboard rear panel we can find two eSATA ports, six USB ports, a gigabit network port, IEEE1394 port and five analogue audio-jacks with an optical SPDIF Out.

You can check out the complete list of mainboard specifications from the table below:

The support of two LGA771 processors requires not only a larger eATX mainboard form-factor. Intel D5400XS also sets specific requirements to the power supply unit. Intel recommends using at least 1kW PSU for Skulltrail platform. However, these requirements are a little bit exaggerated, because with a single graphics card and CPUs overclocked to 4GHz a 600W PSU is more than enough. The really important thing, however, is the presence of two 8-pin 12V power connectors instead of one. Although the board can work fine with only one of them actually used, during overclocking you should better make sure both of them are connected as it will prevent the system from overloading.

Now that we have briefly introduced to you Intel D5400XS, we can finally sum up the main differences between this mainboard and a regular dual-socket LGA771 workstation mainboard and figure out what makes Intel D5400XS a solution for computer enthusiasts:

These three features are the determinative ones. So far there are no mainboards other than Intel D5400XS that could boast the same. And they will hardly ever appear, because the market for Skulltrail type of platforms is still very small.

FB-DIMM Memory

FB-DIMM DDR2 support appeared in Skulltrail platform for a reason. This is a heavy burden inherited from a server i5400B Express core logic set it is based on. But although FB-DIMM slots look quite justified in servers and workstations due to large memory capacities involved, in enthusiasts systems they seem kind of out of place.

Nevertheless, Intel offered us a pair of 2GB FB-DIMM memory modules from Kingston for our Skulltrail tests. These modules worked at 800MHz with 5-5-5-15 timings.

This is the fastest FB-DIMM available today, besides, it is nearly impossible to find in retail. The modules available in the market freely these days usually work at 667MHz only.

However, we decided to give up this memory, because our experiments revealed that quad-channel mode is more efficient than dual-channel mode, even if the memory is working at a lower frequency. Therefore, we performed the tests with four widely spread 667MHz 1GB FB-DIMM modules from Micron.

The modules SPD reports 5-5-5-11 timings:

However, they work just fine with even more aggressive settings, which we have certainly taken advantage of.

As you know, the main peculiarity of fully-buffered DDR2 DIMM modules is the use of serial bus for data transfer between the DDR2 SDRAM chips and memory controller instead of parallel bus. That is why they are completely incompatible with regular unbuffered and registered DDR2 modules. Each FB-DIMM module contains DDR2 SDRAM chips connected to the serial bus via the additional AMB (Advanced Memory Buffer) chip installed onto each module.

There is also another side to this approach. Memory subsystem built from FB-DIMM modules has very high latency that increases because there is an additional AMB chip in the data’s way from the memory chips to the CPU.

For example, here are the results taken from quad-channel memory subsystem built with DDR2-667 FB SDRAM modules with 4-4-4-15 timings:

You can immediately see the bottleneck of the Skulltrail platform: low read speed and high latency. Regular single-CPU desktop systems with DDR2 SDRAM (and especially DDR3 SDRAM) can boast much higher read speed and considerably lower latency.

Moreover, I would also like to say that AMB is a pretty complex device that consumes a lot of power and heats up very noticeably. That is why all FB-DIMM modules as a rule consume about 3-6W each and must be covered with heat-spreaders. During our Skulltrail platform tests we detected memory temperatures of over 70ºC.

No wonder that Intel recommends installing additional fans into Skulltrail systems specifically for memory cooling.

All in all, we can conclude that if Intel continues developing dual-socket systems for computer enthusiasts, their primary focus will be on improving the memory subsystem, no doubt.

Testbed and Methods

It is really hard to find worthy competitors for Intel Skulltrail system. It is a unique high-performance dual-socket solution for home users on two quad-core processors. That is why we have also included the top platform from a totally different category that uses one Core 2 Extreme QX9770 quad-core processor. This comparison would be extremely interesting, since this processor features the same specifications as the Core 2 Extreme QX9775 using in Skulltrail platform.

We have also measured Skulltrail platform performance with a single CPU installed. Although configurations like that are very unlikely to be ever used in reality, the obtained results will help us to estimate how greatly FB-DIMM DDR2 slows down the system and what performance improvement a second CPU in this system can guarantee.

The complete list of our testbed components looks as follows:

We performed the tests with mainboard BIOS setup for maximum performance. We used 64bit applications everywhere where it was possible.


Synthetic Benchmarks: PCMark Vantage and 3DMark06

Formally, PCMark Vantage can only create four computational threads. Nevertheless, Intel Skulltrail system works faster in this benchmark with two quad-core processors. It may be explained by the fact that Vista’s intellectual task manager tries to distribute the threads to physically different processors, which in the end allows using L2 caches of the system shared between the core pairs more efficiently. However, it doesn’t help Intel Skulltrail to outperform a “regular” system with only one Intel Core 2 Extreme QX9770 CPU inside. The reason is simple: inefficient memory subsystem built with FB DIMM modules.

However, 3DMark06 benchmark puts Intel Skulltrail platform with two CPUs on top of their pedestal, which is especially noticeable in CPU test. No wonder, since it is very well optimized for multi-threaded environments, which we have already seen many times in our previous test sessions.

Video Encoding

In fact, most contemporary video codecs can split computational workload into parallel threads quite successfully. However, as we see from the Xvid results, it is not always enough to ensure a significant performance improvement with more processors in the system. The bottleneck for this codec is evidently the memory subsystem, so that a single-CPU system with fast DDR3 SDRAM outperforms Intel Skulltrail. However x264 codec shows a completely different picture. Performance here is highly scalable depending on the number of CPUs in the system.

Image Editing and Non-Linear Video Editing

Although the latest Adobe Photoshop version is optimized for SMP systems, it is actually true not for all operations and filters. Therefore, the results of this test do not really reveal the advantages of 8-core Skulltrail platform over the same quad-core one. So, the winner here is a simple single-socket system with high-performance DDR3 SDRAM.

The results of popular video and non-linear editing applications are also not in Skulltrail’s favor. These applications also know to effectively distribute the workload in multi-processor systems, however our system with a single Core 2 Extreme QX9770 is again faster than Skulltrail. I once again convince myself that FB-DIMM should stay as far away from desktop systems as possible. Otherwise, it threatens to become an inevitable bottleneck limiting the performance in numerous resource-hungry applications.

Final Rendering

Final 3D rendering tasks are traditionally demonstrating almost linear performance scalability from the number of computational cores in the system. No wonder that Skulltrail platform is beyond any possible competition here. The only problem is that rendering is not the main type of applications that would be run on Skulltrail, because gaming enthusiasts are hardly interested in it and professionals dealing with 3D suites would normally have a workstation at their disposal.


Contemporary gaming tests show that Skulltrail is completely out of range here. In all tests we performed, Skulltrail loses to a single-processor system with Core 2 Extreme QX9770 processor. And it happens not only in those games that do not support multi-threading, but also in such titles as Unreal Tournament 3 and Lost Planet: Extreme Condition that are pretty well optimized for multi-core systems. The explanation of this phenomenon is evident: the system should be well-balanced and have no bottlenecks like the memory subsystem in Skulltrail platform, only then it will run fast.

Chess is a completely different type of gaming applications. The computational algorithm in this old strategy game can be split into parallel threads and doesn’t address the memory subsystem too often, which immediately tells on the results. Eight-core Intel Skulltrail system gets significantly ahead of the quad-core systems.

Power Consumption Tests

To complete our article we decided to also measure the power consumption of Intel Skulltrail platform (without the monitor) and compare it against that of a Core 2 Extreme QX9770 based platform. Both systems were configured the same way as during performance tests. The CPUs were loaded with Prime95 25.5 utility.

Although new Intel processors become more and more economical, it seems to be not the case for Skulltrail. There are three factors determining high power consumption in idle mode. Firstly, there are two processors inside. Secondly, this system is equipped with FB-DIMM DDR2 memory that is not economical at all. And thirdly, Skulltrail platform doesn’t support Enhanced Intel SpeedStep technology.

Under heavy workload Skulltrail platform consumes about 400W of power, which is a sort of a record for contemporary desktop systems. Here we should point out that Core 2 Extreme QX9775 processors consume evidently less than 150W TDP. Namely, the difference between the platform with one and two processors is only about 80W.


Since Intel Skulltrail platform is first of all targeted for advanced users, Intel had to make sure that it features the sufficient options for successful CPU overclocking. And it was not only about increasing the processor clock frequency multiplier. LGA771 Core 2 Extreme QX9775 processors, like all other Core 2 Extreme CPU models, boast an unlocked clock frequency multiplier. However, despite this fact, Intel D5400XS mainboard has quite advanced settings for successful CPU overclocking not only through multiplier increase but also by raising the FSB bus frequency.

Let’s check out overclocking friendly BIOS Setup parameters available on Skulltrail platform. All options dealing with system configuring are gathered together in the Performance section of Intel D5400XS BIOS.

Processor Overrides section contains the main parameters: CPU multiplier and FSB frequency. These values are set simultaneously for both processors, which prevents you from overclocking each CPU separately. However, the processor Vcore can be set independently for each CPU. The maximum available voltage setting is 1.6V, plus you can add another 0.3V through CPU Voltage Offset parameter. You can also increase the FSB voltage (up to 1.5V) and chipset North Bridge voltage (up to 1.6V).

Memory Overrides section provides access to memory latencies and voltage. You cannot adjust memory frequency here, it is being set automatically basing on what the SPD reports. Here you can also come across some typical server options such as disabling Snoop Filter and switching the memory controller operational modes.

Bus Overrides section allows adjusting PCI Express bus frequency.

Reference Voltage Override page offers to adjust base GTL and FSB voltages.

We couldn’t pass on the practical experiments revealing the potential of Core 2 Extreme QX9775 CPUs of the Skulltrail platform. Since these processors are based on 45nm cores they should overclock pretty well. For example, similar LGA775 quad-core Penryn processors can easily get past 4GHz frequency with a slight Vcore increase alone.

To ensure proper cooling of CPUs in our Skulltrail platform we use a couple of Zalman CNPS9500 coolers. We checked the platform stability with Prime95 25.5 utility.

As we have expected, Core 2 extreme QX9775 proved up to our expectations. Skulltrail system remained stable with CPU voltage at its nominal level and the multiplier at 9x, i.e. at 3.6GHz CPU speed.

To ensure that the system is stable with the next multiplier setting of 10x, we had to raise the CPU Vcore. The system remained fully stable only at 1.4875V set for both processors.

In this case we overclocked the processors by 25%, i.e. to 4GHz frequency.

We didn’t dare overclock any further because the system heated up severely at 4GHz already: our CPUs temperature read 90ºC.


No one will argue that Intel Skulltrail platform can set the performance in certain applications to a totally new level thanks to 8 processor cores. However, as our tests showed, there are still very few applications like that. Among them are the ones that can not only split the workload between 8 parallel cores efficiently enough but also do not require high memory subsystem performance. These are first of all final rendering applications as well as some video editing and encoding tasks. As for the majority of typical desktop applications, Intel Skulltrail doesn’t look very attractive there at all, falling behind single-processor systems with a quad-core CPU and unbuffered memory.

I would like to specifically draw your attention to the fact that although Intel Skulltrail is being promoted as an extreme gaming platform, its gaming performance is quite disappointing. Most contemporary games cannot load eight processor cores of the Skulltrail platform with work. And slow memory subsystem using FB-DIMM DDR2 modules doesn’t let it even catch up with the single-processor gaming systems.

In fact, the only advantage of the new Intel Skulltrail platform from the gaming standpoint is compatibility with both: SLI and Crossfire technologies. However, it will hardly satisfy those users who will spend a few thousand dollars on it. Especially, since it supports only one version of SLI: with two graphics cards.

However, it is not only the performance in games and other applications that may shake the attractiveness of Intel Skulltrail platform. Even its unbelievably high price of $1500 per Core 2 Extreme QX9775 CPU and $650 for the mainboard is not that upsetting. We have actually expected all of this. It is much worse that Skulltrail doesn’t make the impression of a solution that has been finalized and ready to go into mass production. Now that we have taken a really close look at this system we tend to believe that we still dealt with an engineering prototype, which is quite far from a mass solution.

And the first thing that pushes us towards this conclusion is the memory subsystem. We believe it is Intel’s major strategic miscalculation that they left the Skulltrail memory subsystem in its “server” representation without changing anything. FB-DIMM DDR2 memory modules not only heat up a lot during work and slow the whole system down, they also cannot be overclocked. The Skulltrail mainboard BIOS offers no options for clocking the memory at frequencies other than what SPD states.

The system’s power appetite is also a cause for concern. Two powerful CPUs and FB-DIMM modules push Skulltrail power consumption far beyond that of a system with a similarly performing CPU and faster memory. Besides, Enhanced Intel SpeedStep technology doesn’t work on Skulltrail, which makes this platform completely uneconomical in idle mode.

Skulltrail has no noise-reducing technologies. The mainboard it uses doesn’t allow adjusting any fan rotation speeds, and the chipset fan howls so badly that you will hardly be able to use this system at home.

All in all, we can probably regard Intel Skulltrail as yet another demonstration of Intel’s technological superiority. Maybe, if AMD didn’t give up their dual-socket FASN8 enthusiast platform, Skulltrail could have become much more user friendly. However, now that there is simply no competition, it looks like Intel engineers didn’t want to invest too much effort in adapting server components for desktop use. As a result, the platform we saw today impresses us mostly with its specifications and looks, but doesn’t prove up to our expectations in action.