CES Report: Nvidia Announces Hybrid SLI

Nvidia did its part to contribute to the CES madness by announcing Hybrid SLI, a technology initiative designed to fulfill two missions: Increase graphics-processing power by harnessing motherboard graphics to discrete GPUs, and reduce power consumption when you don't need as much 3D horsepower.

Of course, your motherboard must have an integrated GPU in order to accomplish that trick, so every new Nvidia motherboard—that's right, every new motherboard—will now feature integrated graphics. Unfortunately, environmentally conscious consumers will need to recycle their existing motherboard and videocard in order to take advantage of the new technology. Oh, and the technology will be supported only in Vista: Windows XP hold-outs won't be able to join this green party.

Nvidia has come up with two new names for Hybrid SLI's functions: GeForce Boost and HybridPower. GeForce Boost comes into play when a GPU integrated into the motherboard is coupled with a discrete GPU on a videocard. HybridPower describes the system's ability to shut down the discrete GPU when it's not needed. Nvidia says the discrete GPU doesn't just go into a low-power state; its voltage regulators are actually shut down so that it doesn't draw any power at all.

When you don't need as much graphics horsepower, HybridPower will shut down your discrete GPU and rely entirely on the motherboard's integrated graphics.

A complete Hybrid SLI solution will require both a new nForce chipset and a new GPU (none of which Nvidia was prepared to announce at CES). The first motherboard chipsets featuring Hybrid SLI—the nForce 780a SLI and the nForce 750a SLI—will be designed for desktop AMD CPUs. Intel and notebook PC chipsets will ship sometime in the second quarter. The currently available GeForce 8500 GT and GeForce 8400 GS will support GeForce Boost technology when installed in one of the new motherboards, but not HybridPower. Nvidia's upcoming nForce 730a chipset will support GeForce Boost, but not HybridPower.

HybridPower is fairly simple to understand; GeForce Boost is more complicated. Here's a highly simplified explanation of how it works: Graphics commands are sent to both the discrete GPU and the integrated GPU. Each component renders a frame to its buffer (the integrated GPU will use a segment of system memory for its frame buffer), and then a block-transfer operation copies the image to the display. New nForce motherboards will have integrated analog VGA and digital outputs. Nvidia expects most motherboard manufacturers will use DVI for their digital output, but HDMI is also supported. DisplayPort, on the other hand, is not supported.

GeForce Boost can augment the graphics power of your onboard GPU by harnessing to the discrete GPU running in a PCI Express slot.

One thing Hybrid SLI is not is an enthusiast technology—at least as far as GeForce Boost is concerned. Here's why: As you're probably aware, current SLI configurations require that both videocards be outfitted with the exact same GPU. The reason for this restriction is largely because Nvidia relies on alternate frame rendering (AFR) to achieve the best SLI performance. In AFR mode, one GPU renders one frame while the other works on a second frame. If you chain a high-powered discrete GPU to a slow integrated GPU, you'll slow down the discrete part and slow down the system as a whole.

Enthusiasts can still benefit from Hybrid SLI in terms of power savings: When you're gaming or using your PC for similarly 3D-intensive tasks, the onboard GPU will be shut off; but when you want to switch over to a less-demanding application (web browsing, word processing, or even watching an HD movie), the high-powered GPU (or GPUs, if you're running two-way or three-way SLI) are shut down via HybridPower and you'll save electricity by using the onboard GPU.

You won't need to switch cables, either, because your monitor will remain plugged into the motherboard's video output. What's more, you'll be able to connect a second monitor to the discrete GPU (assuming its running, of course). Nvidia said they're working being able to bring this dual-display technology to conventional SLI, too. As it stands, the monitor plugged into the second or third videocard in SLI will go dark when SLI is enabled.

For me, the most interesting thing about Hybrid SLI isn't HybridPower or GeForce Boost. I'm much more interested in the GPU integrated into these new chipsets. Why? Because I'll be able to build a home-theater PC with a silent GPU that's capable of offloading all HD video decoding chores from the host CPU. I'll never use it for gaming, but I have other machines for that application.