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SLI antialiasing debuts

A new way to double up in graphics

WHEN ATI FIRST ANNOUNCED its CrossFire multi-card graphics platform to the world in late May, the clever folks on the red team had a few interesting new twists to offer in their answer to NVIDIA's SLI. One of the more appealing features of the CrossFire platform was to be a "super antialiasing" mode, allowing two graphics cards to team up in order to produce higher quality antialiasing than available on a single card alone. We liked the idea, noting that "CrossFire rigs may provide image quality benefits even in games where fill rate and geometry throughput aren't normally at a premium." Since there are quite a few current games that don't really take advantage of even a single high-end graphics card, using the extra power of a second card to improve image quality makes sense.

It seems NVIDIA liked the idea, too, since they announced shortly before the launch of the GeForce 7800 GTX that they would be bringing a similar antialiasing mode to SLI systems via a driver update. Now, in an amusing bit of one-upsmanship, NVIDIA is ready to deliver drivers that will make SLI antialiasing widely available today, while ATI's CrossFire platform is still missing in action, apparently delayed.

We managed to snag an early copy of NVIDIA's new drivers and put SLI antialiasing to the test. Keep reading for a look at the image quality and performance of SLI antialiasing, as well as an explanation of the methods behind the madness.

Turning on SLI antialiasing
Before we go on, let me pause to acknowledge that the following discussion will assume a fair amount of prior knowledge of current graphics technology. If you're not up to speed on such things, you may want to read over our initial look at SLI technology and our follow-up article that explains some of SLI's limitations. You'll then probably want to peruse our review of the new GeForce 7800 GTX graphics card, which is currently the most powerful card capable of operating in SLI.

Now, let's dig in.

There are two new SLI antialiasing modes, 8X SLI and 16X SLI. Both are made available on SLI systems after the installation of NVIDIA's new graphics driver. The early driver we tested was version 77.74, but 77.76 is the revision number of the first public release of this driver. Once the driver is installed, you'll have to apply the SLI Coolbits Registry hack in order to see SLI antialiasing as an option. To enable one of the SLI AA modes, the user must pick "SLI antialiasing" from the list of SLI rendering modes in the NVIDIA control panel, like so:

Once SLI AA is enabled, the user can then choose either 8X or 16X mode via the antialiasing slider.

If that method of enabling SLI AA seems a little convoluted to you, rest easy. NVIDIA says it has plans to integrate access to the SLI antialiasing modes more organically into the regular AA-mode slider in the control panel.