We recently had an opportunity to question NVIDIA about their newly announced Hybrid SLI Technology. Today's questions are answered by NVIDIA's Tom Petersen, who is their Director of Technical Marketing. Although this question and answer session only skims the surface of Hybrid SLI, it does serve as general introduction to the technology and is supplemented with visual aids.

nV News: What is Hybrid SLI?

Tom: Hybrid SLI is a new PC technology comprised of two features delivered when selected GeForce motherboards are combined with GeForce GPUs on graphics cards. The first feature is GeForce Boost, which increases overall graphics performance up to 80%. HybridPower is the second feature, which allows users to shut off the graphics card when not needed and dramatically reduce power consumption. Taken together these two features make Hybrid SLI a key technology in both mainstream and enthusiast users in both desktop and notebook PCs.

Like SLI technology, Hybrid SLI uses two or more GPUs to work its magic. The difference with Hybrid SLI is that one of the GPUs is a motherboard GPU (mGPU) built on to the motherboard, which is like integrated graphics but with better performance, DirectX compatibility and HD movie playback. The motherboard GPU is paired with one or more discrete GPUs via graphics cards.

NVIDIA Hybrid SLI Technology

nV News: How does GeForce Boost increase performance?

Tom: 3D graphics are generated on a PC much like a movie. A series of frames are dynamically generated, or rendered, and then displayed on the monitor. The sequence of rendered frames gives the impression of motion to users just like a movie. NVIDIA's SLI technology uses a technique called Alternate Frame Rendering (AFR) to distribute to job of rendering this series of frames across multiple GPUs. With AFR, each GPU takes on the task of rendering every other frame. Working in tandem, 2 GPUs produce more frames and deliver a more fluid experience.

Hybrid SLI's GeForce Boost does exactly the same thing. Of course it is not quite that simple though. GeForce boost accounts for the different processing capabilities of each GPU and can produce different rendering sequences of AFR to deliver the best performance. Depending on the model of motherboard GPU and discrete GPU, users will see up to an 80% performance increase over the graphics card alone.

NVIDIA GeForce Boost

nV News: How does the HybridPower power-saving feature work?

Tom: When users are doing simple tasks, like email or watching a movie, they don't need the horsepower of the graphics card's discrete GPU. In that case HybridPower allows a user to shut down the discrete GPU and use the mGPU to do all graphics processing work.

NVIDIA HybridPower

nV News: How much power can HybridPower save?

Tom: That depends on the graphics card. Even though the graphics engine is not doing much when a PC is idle, the graphics card can still consume up to 100 watts. Even more power is consumed when multiple graphics cards are in a system. Since HybridPower can work with multiple graphics cards, in a 3-way SLI system a user can save 300 watts, which can save up to $20 a month.

HyBridPower Can Shut Off GPUs

nV News: Why did NVIDIA develop Hybrid SLI?

Tom: The idea was conceived back when we created NVIDIA SLI technology which was launched in 2004. With gaming graphics cards getting more power hungry and energy costs rising, it was obvious we needed to do something to curb power consumption. And now with Windows Vista and a trend towards 3D in common applications, it is clear more graphics horsepower is needed for mainstream consumers. With Hybrid SLI we solve both problems.

Like SLI technology, Hybrid SLI uses two or more GPUs to work its magic. The difference with Hybrid SLI is that one of the GPUs is a motherboard GPU built on to the motherboard, which is like integrated graphics but with better performance, DirectX compatibility and HD movie playback. The motherboard GPU is paired with one or more discrete GPUs via graphics cards.

HyBridPower Can Lower Acoustics

nV News: What were the challenges behind developing Hybrid SLI?

Tom: The biggest challenge was engineering the software drivers. GeForce Boost is similar to our multi-GPU SLI technology, which is very robust so that work was more straightforward. The only major innovation required for GeForce Boost was making different GPU types cooperate together – powerful discrete GPU scales well with a smaller motherboard GPU.

HybridPower was more challenging. Seamlessly switching between the motherboard GPU and discrete GPU and getting Windows Vista to play along is very difficult since Hybrid Power requires the entire GPU context to be moved between different GPU types. This is sort of like translating a major novel back and forth between French and Spanish on every Hybrid transition. However, our engineering team came through and we'll be saving lots of kilowatts this summer.

nV News: What hardware components does HybridPower currently support?

Tom: Our GeForce 8200 and soon to be released nForce 780a and 750a motherboards support Hybrid SLI. These are AMD platforms. Motherboards for Intel CPUs are coming this Summer. The recently released GeForce 9800 GTX and 9800 GX2 graphics cards support full Hybrid SLI. Older 8400GS graphics cards will work in GeForce Boost mode.

NVIDIA nForce 780a SLI Architecture

nV News: What operating systems does HybridPower currently support?

Tom: Only Windows Vista is supported at this time.

nV News: What is role of the motherboard GPU when HybridPower is being used?

Tom: It handles all of the graphics and video processing. It is a true GPU with full DirectX 10 support and enough graphics performance for mainstream games like World of Warcraft or Second Life. It has a dedicated PureVideo HD video processing for HD movie playback.

nV News: Is HybridPower enabled automatically does it require some sort of manual intervention?

Tom: Initially, the modes will be selected via an easily accessible software utility in the taskbar that allows users to choose performance or power saving mode. Eventually we'll add an auto mode that dynamically switches modes based on the needs of the applications that the user is running. Of course, the user will be still be able to manually select the mode if they like.

Hybrid SLI Technology User Interface

Hybrid SLI Technology User Interface

nV News: Will Hybrid SLI motherboards eventually support HDMI output?

Tom: There are already Hybrid SLI ready motherboards that have HDMI. The two technologies work together. It is up to the motherboard maker to decide if they want add HDMI. HDMI can be supported off the motherboard GPU or the discrete GPU, or both.

nV News: What is the future of HybridPower?

Tom: Look for new Hybrid SLI motherboards for AMD CPUs on the shelves around the end of April. In the future we'll give users to option to automatically switch between performance and power-saving modes. Hybrid SLI motherboards for Intel CPUs will arrive this summer. We'll also see Hybrid SLI notebooks that use GeForce Boost for better visual performance and Hybrid Power for better battery life.

Availability

Beyond that we need to be a little less specific, but it is safe to say that multi-GPU technologies like Hybrid SLI are very important to NVIDIA. We will continue to make visual computing more compelling and more seamless using Hybrid SLI technologies.

nV News: We would like to thank NVIDIA and Tom for taking the time to answer our questions in regards to this exciting technology. We are certainly looking forward to working with and reporting on NVIDIA's HybridSLI Technology in the upcoming months!

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