Getting Started with 3-Way SLI

The components

So what will you need to run a 3-Way SLI system? Have a look at the following guidelines:

GeForce 8800 GTX or GeForce 8800 Ultra GPU:

To date, NVIDIA’s GeForce 8800 GTX and 8800 Ultra are the only GPUs with two built-in SLI headers, located on the top edge of the graphics card above the fan. Even the recently released GeForce 8800 GT and GTS 512MB only sport one SLI header. NVIDIA has developed a new 3-Way SLI connector which must be connected to the headers on the graphics cards in order for 3-Way SLI to operate properly.

Now in theory you could use the PCI Express interface to link three cards together for 3-Way SLI without the connector, say for instance if you wanted to link three GeForce 8800 GTs, but the current 3-Way ForceWare 169.18 driver is limited to supporting just the GeForce 8800 GTX and Ultra GPUs only. We know because we tried running 3-Way 8800 GTS and GT SLI as an experiment once we were finished with our 3-Way GeForce 8800 Ultra testing.

You really wouldn’t want to do this anyway; over the course of our testing for this article our SLI cable actually came loose when running 2-Way tests and the cards weren’t scaling properly as a result: we were seeing 2-Way SLI performance improvements of 20-30% when the difference should have been closer to 50%. Going from two to three cards, the PCI Express interface would have likely been even less effective.

With three GeForce 8800 GTX or Ultra cards running in sync together, we should also point out that you’ll want a powerful CPU to keep everything running smoothly. Fortunately most Core 2 CPUs can be overclocked to speeds of 3.0GHz or greater with ease, so this shouldn’t be a problem for most enthusiasts.

Finally, all three cards don’t have to come from the same board manufacturer. You can mix and match cards however you’d like, with the only limitation being that they must all be based on the same GPU (i.e. you can’t mix a GeForce 8800 GTX with a pair of GeForce 8800 Ultras).

1-kilowatt (1,000W) Power Supply with 6 six-pin PCIe connectors or 4 six-pin connectors and 2 8-pin connectors recommended; 1.1KW power supply if running a quad-core CPU:

At a minimum, NVIDIA recommends a 1,000W power supply for 3-Way SLI for those of you with dual-core CPUs, if you’re running quad-core, NVIDIA bumps the minimum recommendation up to 1,100W. You’ll also need to make sure that your power supply has either 6 six-pin PCIe connectors or 4 six-pin connectors and 2 8-pin connectors in order to hook all three graphics cards up properly. NVIDIA will be providing a list of compatible power supplies on slizone.com.

Windows Vista:

3-Way SLI is not supported under Windows XP, just Windows Vista.

NVIDIA nForce 680i or nForce 780i Motherboard:

As of today, the only chipset with official 3-Way SLI support is NVIDIA’s nForce 680i SLI MCP. NVIDIA’s upcoming nForce 780i chipset will also support 3-Way SLI when it’s released, as well as PCI Express 2.0, but that’s not today.

3-Way SLI connector:

As we mentioned above, 3-Way SLI requires the use of a new 3-Way SLI connector which is pictured below. Users with an nForce 680i motherboard will have to purchase this new connector in order to get 3-Way SLI up and running properly. We’ve been told that the 3-Way SLI connector should retail for $20.

Case with good airflow:

Obviously with three high-end GeForce 8800 GTX or Ultra cards sitting in such close proximity to one another it’s imperative that you select a large case and equip it with good cooling. In fact, NVIDIA’s reviewer’s guide states: “We recommend that users select chassis that allow placing fans on the front, on the back, and on the side of the chassis pointing at the GPUs. This configuration helps create proper pressure within the chassis to allow the hot air to exit.” So far, NVIDIA has approved two cases for use with 3-Way SLI, the Cooler Master Cosmos and the Silverstone TJ10.