Do-It-Yourself Quad-SLI: It's Official
Quad-SLI Components: Mobo, CPU & PSU
Quad-SLI's motherboard requirements are similar to a standard SLI system. However, we should note that the GeForce 7950 GX2 does not require a full PCI Express x16 electrical connection to function properly; a pair of 7950 GX2s will function in older nForce 4 SLI based motherboards. Because the traffic coming in is already comprised of 8 lanes on some SLI chipsets (from the chipset splitting a 16 lane PCIe connection into two 8 lane connections going to each PEG slot), the NVIDIA designed PCI Express switch used on the 7950 GX2 will interface with the 8 lane connection to the chipset, and just pass 8 lanes worth of traffic to each addressed GPU as needed. Technically Quad-SLI will work on all SLI capable chipsets like the NF590 SLI, 570 SLI, NF4 SLIx16, and standard NF4 SLI.
Although the NVIDIA PCI Express switch is compliant with the standard PCI Express specifications, the system BIOS of some motherboards may not properly recognize the 7950 GX2 right away. This was one of the hurdles NVIDIA wanted to overcome before endorsing DIY Quad-SLI. Without a properly configured system BIOS, the motherboard could fail to post or may not operate reliably with a 7950 GX2 installed. NVIDIA informed us that they have been working closely with motherboard manufacturers to have their system BIOSes updated to support the GX2, however. Refer to this site for a list of known compatible motherboards and the proper BIOS revisions that have been tested by NVIDIA. But please note the list on that site is not inclusive of all compatible motherboards, but rather reflects motherboards that have already been tested and qualified by NVIDIA. And don't be confused by the Intel and ATI-chipset based motherboards listed on that page. Those motherboards will work with a single 7950 GX2, but they are not Quad-SLI certified.
The motherboard that we used for our Quad-SLI project, the Asus P5N32-SLI SE Deluxe, was based on the NVIDIA nForce 4 SLIX16 Intel Edition chipset. The Asus P5N32-SLI SE Deluxe is a new revision of a motherboard that we've already reviewed here at HotHarware, the P5N32-SLI Deluxe. The P5N32-SLI SE Deluxe is essentially revision 2.02G of the P5N32-SLI Deluxe. The majority of the motherboard was unchanged, but the P5N32-SLI SE Deluxe has an updated Quad-SLI compatible BIOS and a revamped VRM to fully support Intel's Core 2 Duo and Extreme processors.
The Asus P5N32-SLI SE Deluxe features true dual-PCI Express x16 graphics slots allowing full bandwidth SLI / Quad-SLI. The PEG slot closest to the CPU socket is the primary graphics slot, and it's separated from the secondary PEG slot by a PCI Express x1 slot and a PCI Express x4 slot. Installing a pair of GeForce 7950 GX2 cards into the P5N32-SLI SE Deluxe is the first step towards a Quad-SLI system. With the cards installed though, clearance is a bit tight in some areas, like near the SATA connectors for example.
A Quad-SLI system also requires a powerful processor to feed its GPUs. AMD's Athlon 64 FX processors and Intel's Core 2 Duo / Extreme are currently the best choices for a Quad-SLI system in our opinion. For our build, we used Intel's flagship Core 2 Extreme X6800 processor. As of today, this is the most powerful desktop processors available. We recently evaluated the Core 2 Extreme X6800 and Core 2 Duo E6700. If you'd like to delve a little deeper into the inner workings of these processors, click here.
With four GPUs and a powerful processor at its heart, a Quad-SLI system has some lofty power requirements. Each GeForce 7950 GX2 can consume a peak of approximately 143 watts of power. Double that number, and account for a CPU, RAM, hard drives, a motherboard, and a myriad of other components and you quickly realize that a run-of-the-mill power supply will not be able to meet the demands of a typical Quad-SLI system. For our build we used a PC Power and Cooling 1 Kilowatt (1000 watt) unit, but there are others available that would have worked just as well. A list of certified power supplies is available on NVIDIA's SLIZone website. When shopping for a Quad-SLI capable PSU, it's best to look for a model that has multiple 12v rails that can each meet the current demands of Quad-SLI. It's not just about total wattage.