SLI support, segmentation, and performance

Unfortunately, not every PCI Express NVIDIA graphics card will take advantage of SLI. NVIDIA’s GeForce PCX line doesn’t support this new technology, GeForce 6800 is the first to provide this capability.

PCI Express GeForce 6800 Ultra reference board

The back of the reference card

NVIDIA is focusing on the $299 and up segment of the 3D market. There are no current plans to bring SLI to the mainstream and value segments. This ensures that you can’t purchase two $200 mainstream GeForce 6 boards to equal the capability of one $400 GeForce 6800 GT or a $500 GeForce 6800 Ultra. Additionally, another requirement of SLI is that both cards must come from the same manufacturer and be based on the same configuration. For example, you can’t combine a 128MB GeForce 6800 with a 256MB GeForce 6800 board, or a GeForce 6800 GT with a GeForce 6800 Ultra.

Besides the GeForce 6800 line, NVIDIA also plans to bring SLI to the workstation market with its line of PCI Express-based Quadro cards. The concept is the same, only you’re dealing with Quadro FX 4000 instead of the GeForce 6800 series.

Quadro PCI Express card

Quadro boards are linked together

Quadro up and running in the system

Quadro PCI Express reference board

Other important details

SLI is completely invisible to the end user; no special driver is required for operation. In fact, SLI users will download the same driver as every other NVIDIA user. Likewise, games don’t have to be programmed to take advantage of SLI, but some games will see larger gains than others. NVIDIA has witnessed improvements of up to 1.87 times over a single graphics card in 3DMark 03 (tested at 1600x1200 with 4xAA and 8xAF in game tests 2, 3, and 4) and Epic’s Unreal Engine 3 at 1024x768. We wouldn’t be surprised if flight simulation titles, which tend to be more platform-bound than other genres, saw lower performance improvements.

To further improve performance, NVIDIA will also be seeding developers with hardware and providing their SLI algorithms to programmers so they can code for it, but NVIDIA made it clear that you won’t see an exact 2x performance improvement, at least with first generation hardware.

It’s also important to keep in mind that NVIDIA SLI isn’t Alienware’s previously announced X2 video array technology. While the underlying technique is somewhat similar, the execution is different. Alienware’s X2 requires a third external card, the video merger hub, to communicate between both cards, and works for both ATI and NVIDIA hardware, including the GeForce PCX 5900.

NVIDIA is offering its SLI technology to all of its customers, including Alienware, so there’s nothing stopping Alienware from adopting the technology in their own systems.