Setting up a three-way SLI rig with GeForce 9800 GTX cards isn't all that different than it is with GeForce 8880 Ultras. For the 9800 GTX, we chose to upgrade from an nForce 680i SLI-based motherboard to a 780i SLI mobo in order to gain support for PCI Express 2.0. As we've explained, the nForce 780i SLI's PCIe 2.0 is a little odd since it uses a PCI Express bridge chip, but Nvidia claims it should be adequate. The most ideal configuration would probably be a board based on the nForce 790i SLI, but I didn't have one of those handy.
You will need some specialized hardware in order to make a setup like this go. In addition to the motherboard and graphics cards, you'll need a three-way SLI connector like the one pictured above, which you may have to order separately. This connector snaps into place atop all three cards, connecting them together. You'll also need a power supply with six auxiliary PCIe power connectors and sufficient output to power the whole enchilada. I used a PC Power & Cooling Turbo-Cool 1200 that's more than up to the task.
We used the same basic building blocks for our quad SLI test rig, but we swapped out the 9800 GTX cards for a pair of GeForce 9800 GX2s from Palit and XFX. We tested the XFX card in our initial GeForce 9800 GX2 review. As you may have learned from that article, each of these cards has two G92 GPUs on it. They're also not cheap. The Palit card is currently going for $599 on Newegg, although there's a $30 mail-in rebate attached, if you're willing to jump through that particular flaming hoop.
Since the GX2 really packs 'em in, a quad SLI setup actually requires fewer power leads and occupies less slot space than a three-way config. Quad SLI also avoids that middle PCIe slot on all capable (nForce 680i, 780i, 790i) motherboards. That slot could be a bottleneck because its 16 lanes of first-gen PCIe connectivity hang off the chipset's south bridge.
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