Related Articles

Scalable Link Interface

Scalable Link Interface (SLI) is one of the biggest bombshells that NVIDIA has dropped on the community in the last few years. Those who are not familiar with SLI technology can take a quick browse through our SLI coverage from a few months ago. The Cole's Notes version of SLI is this: NVIDIA has a technology that allows the use of two video cards to nearly double performance in video limited situations. There are a few catches -

• This is a PCIe Only technology
• This will only work on some cards (6800 Ultra, 6800 GT, 6800, 6600GT)
• Officially, two of the same cards from the same manufacturer are required

We refer back the features chart - note that both the SLI and Ultra versions of the nForce 4 have 20 lanes, the difference being the lanes on the Ultra are fixed whereas on the SLI they are configurable.

For the nForce 4 SLI, the graphics portion of the slots can run in two modes, x16 in single card mode while in SLI mode there are two x8 slots available. There is a physical switch on the motherboard to change the functionality from 1x16 to 2x8. NVIDIA has claimed that the dual x8 lane setup gave the best performance from internal testing. The final piece required for SLI is bridge piece that connects to the MIO connector on each graphics card.

Here are some numbers provided by NVIDIA from a Athlon 64 4000+ system with the 66.72 drivers and a preproduction nForce 4 SLI board.

Note that in Halo and 3DMark05, we have a pair of 6600GTs outperforming a single 6800 Ultra. This makes for some interesting upgrading possibilities down the line. NVIDIA's stance was that they'll be selling a second GPU regardless of whether it is a SLI twin for an existing card or one of their next generation cards so they are not particularly concerned about product overlap.

MSI's SLI Board

As an addendum, it is pretty amazing that NVIDIA's SLI announcement has driven pretty much every single chipset manufacturer to announce dual PCI x16 motherboards for the Athlon 64 market with the exception of ATI. There have been pundits claiming that SLI is only a gimmick but it looks like NVIDIA was correct in saying that there will be wide support for it across the board. They were quick to point out however, that there exists only two chipsets that is validated for SLI, NVIDIA's own nForce 4 SLI and Intel's Tumwater chipset. Whether validation from NVIDIA will be a concern should be revealed in the upcoming months.