NVIDIA SLI Interview

NVIDIA SLI Interview

Written by John Yan on 9/10/2004 for

When Alienware displayed their Video Array system, I was wondering when someone else would be releasing a product with a similiar feature. NVIDIA didn't take too long to unveil their SLI solution. With that, we talked with the Desktop Graphics Product Manager at NVIDIA, Steve Sims.



GamingNexus: What is your reaction to Alienware’s announcement knowing you had SLI in the back of your pocket and only letting it out in the recent month?

Steve Sims: We are working very closely with Alienware and are extremely excited that they are pushing multi-GPU technology forward.


GamingNexus: I’ve heard that Alienware did consult with you when they were developing their Video Array technology. Were they ever aware of your plans to incorporate SLI technology in the PCI-E GeForce 6800 cards?

Steve Sims: Clearly, enthusiasts PC builders are key customers for SLI technology, so we brought in our key partners very early in the process. We were working very closely with Alienware and will continue to do so.


GamingNexus: While the Alienware technology isn’t currently in production, they claim there’s a 50 – 100% increase in performance depending on the article you read. What is NVIDIA’s estimate on how much of an increase you can get in your technology?

Steve Sims: The amount of performance improvement will depend on the application. In some circumstances it is up to a 2X increase in performance. We expect performance to scale almost linearly, and in general, performance gains will be best with applications and modes that tend to be most graphics limited, i.e, higher resolutions with higher levels of antialiasing and anisotropic filtering. We should note that the current performance numbers that Alienware has announced do not reflect any of the dedicated scalability logic, inter-GPU digital interface or dynamic load balancing software of SLI.


GamingNexus: How long has SLI technology been in the works?

Steve Sims: Graphics chips back to GeForce 3 have supported multi-GPU configuration, but we did not enable it until recently.


GamingNexus: What were some large hurdles you had to overcome when doing R&D?

Steve Sims: NVIDIA SLI can intelligently combine and scale graphics performance by having multiple NVIDIA GPU’s in a single system. SLI works by intelligently scaling geometry and fill rate performance for two GPUs. So getting the right algorithms to balance the workload and get maximum performance was the key. There are several methods that can be employed to improve performance when using SLI Technology and the NVIDIA drivers utilize the most appropriate method depending on the needs of the application. At the most basic level, inter and intra-frame scalability algorithms are supported. Details of the specific algorithms are NVIDIA Intellectual Property, so we can not go into much detail.
GamingNexus: How does the technology work? Is it all hardware based or is there a software component?

Steve Sims: SLI takes the PCI Express multi-GPU configuration to the next level because it features intelligent patent-pending hardware and software technology. We have dedicated scalability logic in each GPU and a digital interface between GPU's to help enable this. . In addition we have a full software suite that enables dynamic load balancing and advanced rendering algorithms that provide the best image quality and performance.


GamingNexus: On the surface, how is the process compared to Alienware’s where it load balances the rendering between the two cards.

Steve Sims: The Alienware solution they announced does not take advantage of any of the dedicated scalability logic, inter-GPU digital interface or dynamic load balancing software of SLI.


GamingNexus: Is this something you couldn’t do with AGP or did you just see a new opportunity with the new bus technology?

Steve Sims: The AGP bus was not conducive to an SLI configuration. AGP is not really setup to feed multiple GPU’s data at the speeds necessary to make SLI work efficiently


GamingNexus: Will this work with any new PCI Express board or will this require specialized motherboards?

Steve Sims: SLI technology requires a PCI Express motherboard with two x16 physical connectors. The graphics cards plug into these connectors. The graphics cards can work with whatever routing because x16 PCI Express connectors can auto-negotiate down to x8, or x4 electrical. “SLI Ready” PCI Express motherboards will also be available soon from: Abit, ASUS Computer International, Epox, Gigabyte Technology, Co., Ltd., SuperMicro, Tyan, and Micro-Star International. We will also be supporting SLI on our nForce platforms in the near future.


GamingNexus: Did you use any knowledge from the 3Dfx method or is this all a completely new design scheme?

Steve Sims: This technology was developed entirely at NVIDIA. Many of the engineers are former 3dfx employees, though.
GamingNexus: What has the public reaction been to SLI since you’ve announced it? And how do you think the audience will react once they get their hands on the cards?

Steve Sims: The excitement around SLI has been awesome. People love SLI technology and recall the performance gains from 3dfx days. We have been showing SLI systems in action at select gaming events and people are really craving an NVIDIA SLI system.


GamingNexus: There’s been some large debate in the past years about ATI taking the crown in terms of being the king of video cards from you. How do you think SLI and the 6800 series positions you in terms of the race between you two?

Steve Sims: ATI is a strong competitor, but NVIDIA has always been the technology leader in the graphics industry. Whether you are talking about transform & lighting, programmable vertex shaders, programmable pixel shaders, or 128-bit floating point precision, every revolutionary 3D graphics innovation in the last 5 years has been introduced first on NVIDIA GPUs. We are driving the industry.

The Radeon x800 series is a nice spin of an old architecture, which means they do not have a lot of headroom left in the architecture like NVIDIA does with our brand new GeForce 6 architecture. We will get faster and faster with each driver revision. The reviews on the high-end show that the match-up is very close, but ATI is missing many key next-generation features like 64-bit blending/ texturing and DirectX 9.0 Shader Model 3.0 support. The GeForce 6800 GT is winning in reviews against the x800 Pro at $399, and ATI does not seem to have an answer for the GeForce 6800 at $299. We are really pleased with our GeForce 6 line-up.

Also I have not heard anything about a multi-GPU set-up from ATI.


GamingNexus: When will the cards capable of SLI be available in stores?

Steve Sims: Initial roll-out is targeted at System Builders. Retail versions of SLI-bundled graphics boards will be available later this Fall.


I'd like to thank Steve Sims for taking the time to answer our questions. If you would like to read about the Video Array system from Alienware, be sure to check out our interview with Brian Joyce.

* The product in this article was sent to us by the developer/company for review.


About Author

I've been reviewing products since 1997 and started out at Gaming Nexus. After writing for a few different sites that went under, it's nice to bring back a site that's not dependent on revenue and just wants to deliver news and reviews of products.

I'm  married, and enjoy first person shooters, sports games, and real time strategy games.


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