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Quad SLI under the microscope

Are four heads really better than two?

OVER THE PAST few years, we've seen an incredible number of extreme hardware solutions marketed to PC gamers: graphics cards that cost over five hundred bucks, thousand-dollar "Extreme Edition" CPUs, motherboards with more ports than Dubai, custom physics processors, and now even a "killer" NIC. Without a doubt, though, the most extreme of all of these offerings has to be Nvidia's vaunted Quad SLI. The concept of running four GPUs together for insane gaming goodness is more extreme than snowboarding down some wicked moguls into a vat of Mountain Dew at the X Games.

But does Quad SLI live up to its practically built-in hype? Can running four GPUs in tandem catapult you into a zone of pure extremeness, where new frames flow like water, object edges are feathery smooth, and textures are so perfectly mapped to surfaces that you're utterly convinced they're real?

I dunno. I'm just making this stuff up as I go along. But we have tested Quad SLI in order to see what it's like to play games on a quad-GPU system. We've also popped open the metaphorical hood on Quad SLI to see how it works. Along the way, we found a few unexpected things, as well.

Quad SLI basics
You may remember the 7950 GX2 from our review of it a while back. The GX2 has two G71 graphics processors onboard, each with its own 512MB pool of memory. This product is essentially "SLI on a stick," a dual-GPU solution that plugs into a single PCIe x16 slot. All by itself, the GeForce 7950 GX2 is the fastest "single" video card on the market. Quad SLI involves taking a pair of these cards and running them together in an SLI configuration, bringing the grand totals involved to four G71 GPUs, 96 pixel shader processors, 2GB of DDR3 memory, 153.6 GB/s of memory bandwidth, and over $1100 in video cards alone.


We wanted to outfit our test system with this outrageous config, and we already had a BFG Tech 7950 GX2 from our initial GX2 review. Fortunately, MSI offered us its version of the GeForce 7950 GX2 for review, and we were in business.

MSI's GeForce NX7950GX2. Note the distinctive MSI sticker.

As you might have guessed, the MSI NX7950GX2 is quite a nice video card. It comes with all of the requisite cables and plug converters, has HDCP support, and ships with CyberLink PowerCinema for movie playback. MSI also includes a copy of the King Kong movie game, just to make a point. We had no problem throwing this card into a Quad SLI configuration with our BFG Tech card. (SLI brand commingling has been kosher for a while now.)

You will need an exceptionally fast CPU and an SLI-ready motherboard for a Quad SLI rig. We chose the Asus P5N32-SLI SE Deluxe for its ability to host an Intel Core 2 Extreme X6800 processor. The other big concern with Quad SLI, naturally, is finding an adequate power supply. We chose an OCZ GameXStream 700W PSU for our test system, which just so happens to be on Nvidia's list of SLI-certified PSUs. I would give you some more general PSU specification recommendations for Quad SLI systems, but Nvidia seems to prefer pointing folks to its list of certified power supplies for this application.

With this bundle of components, we were able to set up a Quad SLI system with relatively little drama. Unlike some early Quad SLI configurations that came from system builders, going quad with a pair of GX2s requires only one SLI bridge connector between the two cards.