Do-It-Yourself Quad-SLI: It's Official

Of course, the main components in a Quad-SLI system are the GeForce 79050 GX2 video cards. For the purposes of this article, we got our hands on a pair of XFX GeForce 7950 GX2 cards.  If you've seen the 7800 GX2 and 7900 GX2 boards used in the first Quad-SLI systems mentioned on the previous page, you'll immediately notice that the GeForce 7950 GX2 is significantly smaller and more streamlined. In fact, the 7950 is about the same size as a single-GPU based 7900 GTX at approximately 9" long. The 7950 GX2 also has only one SLI connector at the top, as opposed to the two found on earlier 7800 / 7900 GX2s.

The GeForce 7950 GX2 is equipped with two GeForce 7950 GPUs, each coupled to 512MB of fast GDDR3 memory, for a grand total of 1GB of frame buffer memory per GX2. The 7950 GPU is based on the same G71 GPU used on the 7900 GTX; it's just clocked a bit lower. NVIDIA's reference 7950 GX2 specifications call for a 500MHz GPU clock with 600MHz (1.2GHz DDR) memory. XFX offers a couple of models, however, including the 570M XXX that's clocked much higher at 570MHz / 775MHz (1.55GHz DDR).

   
A Pair of XFX GeForce 7950 GX2 Cards

As we've mentioned, each GeForce 7950 GX2 is built from a pair of PCBs linked together through a proprietary interface. The two GPUs and on-board memory are outfitted with their own slim coolers. The GeForce 7950 GX2 requires only a single 6-pin PCI Express power feed, and cards feature a pair of dual-link DVI outputs along with an S-Video / HD component output. To use the GX2 in multi-monitor mode, however, multi-GPU mode must be disabled in the drivers, just like SLI.

Installing a pair of GeForce 7950 GX2 cards into a system and enabling Quad-SLI isn't just about framerate performance, however.  With Quad-SLI NVIDIA also introduced a new anti-aliasing mode, namely SLI32XAA.  SLI32XAA can be used in conjunction with 16X anisotropic filtering, to offer increased image quality in games that are CPU bound by such a powerful graphics sub-system. And Quad-SLI will also gives users the ability to play games at exceedingly high resolutions, which brings us to our choice of monitor.

   
Dell's 30" 3007FPW

To put it simply, Quad-SLI is not meant to be used with smaller monitors, or monitors that do not support ultra-high resolutions. If you've got a small monitor and don't plan to upgrade, stick with a single video card or a more mainstream SLI / CrossFire configuration.  Quad-SLI will work with virtually any monitor, but if its not capable of running at a high resolution, like 1920x1200 or 2560x1600, for example, there's really no point in using Quad-SLI.  At mainstream resolutions, a Quad-SLI system will typically be CPU-bound, and the graphics cards will not be fully utilized.

Based on our experience with Quad-SLI, we'd recommend using a monitor no smaller than 24" and a resolution no lower than 1920x1200.  In some circumstances, a monitor capable of 1600x1200 will be acceptable, but only if the user planned to use higher-levels of anti-aliasing and anisotropic filtering.  We went right to the top of the heap and acquired one of Dell's huge 3007FPWs.  The 3007FPW features a 30" LCD with a native resolution of 2560x1600.

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