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A new technology that allows a PC to use two PCI Express graphics boards in tandem delivers the fastest graphics performance we've ever seen. We tested a system built with NVidia's SLI (Scalable Link Interface) technology and saw a dramatic performance boost in newer games played at high resolutions--though older, less graphics-dependent games showed little or no benefit.

SLI's Speed Boost

Alas, SLI isn't something you can graft onto your current PC. You'll need a new SLI-ready motherboard featuring NVidia's own NForce4 PCI-Express chip set for Athlon 64. Four NVidia PCI Express graphics cards currently support SLI: the midprice $200 GeForce 6600 GT; and the high-end 6800, 6800 GT, and 6800 Ultra models, which cost between $300 and $500 apiece. In addition, Alienware makes a $6000 dual-Xeon SLI PC, and Gigabyte has been developing an SLI motherboard based on Intel's 915 chip set. NForce boards built to work with Intel CPUs are still a few months away from readiness.

We tested a preproduction Asus A8N-SLI Deluxe motherboard with 6800 GT cards in both single and dual (SLI) configurations, using an ATI X800 board as a reference point. Older games such as Return to Castle Wolfenstein, Commanche 4, and Unreal Tournament 2004 depended less on the graphics board, and they showed little or no performance gain with SLI. In some cases, the SLI setup ran a frame or two per second slower than the system configured with the single card--most likely due to SLI overhead.

With newer GPU-centric games like Doom 3, Halo, and Far Cry, SLI showed a noticeable but inconsequential improvement in frame rate at 1024 by 728 resolution. When we expanded the pixel grid to 1600 by 1200, however, SLI strutted its stuff--offering gains of up to 56 percent over the single-card setup with antialiasing enabled.

All in all, SLI delivered the fastest graphics performance we've ever tested. A completely loaded SLI system is expensive, but if you're buying or building a new PC, it's nice to know that you could dramatically enhance its graphics performance by adding a second card later.

And if even an SLI system isn't fast enough for you, you can milk every last drop of speed out of your system by using NVidia's NTune; this downloadable utility works with NForce motherboards to permit you to overclock your system--that is, run its memory, graphics card, and buses at faster-than-standard clock speeds. NTune will benchmark and automatically adjust your PC for best performance, or you can tweak individual settings as you see fit.

Overclocking

Using NTune on a preproduction MSI K8N Neo4 Platinum NForce4 graphics card, we were safely able to increase our test system's graphics performance by almost 3 percent (gauged conservatively) for gaming and then to reduce performance by nearly 3 percent so the PC could run cooler and quieter, and use less energy while we played DVDs or downloaded large files. Once you've perfected your settings, you can save them for future use. NTune also lets you monitor your PC's temperatures and voltage--an essential feature for debugging overclocking settings.

SLI Boosts Graphics Speed