NVIDIA announces Hybrid SLI, new chipsets

Nvidia took advantage of the mass of press descending on Las Vegas for CES to hold a pre-show briefing unveiling Hybrid SLI. This Windows Vista-only technology seeks to exploit systems running Nvidia integrated graphics chipsets and discrete GPUs, allowing the two to work more closely together to improve performance and lower power consumption. Integrated graphics processors (IGPs) have traditionally been confined to budget chipsets, but that won't be the case any longer. Starting this quarter, all new Nvidia chipsets for AMD processors will include an embedded graphics processor. All new chipsets for Intel processors will start getting integrated GPUs in the second quarter of this year.

To begin, Hybrid SLI will be made up of two components: HybridPower and GeForce Boost. HybridPower is easily the most interesting of the two, allowing a system to literally shut down its discrete graphics cards when their pixel-pushing horsepower isn't needed, deferring to the chipset's integrated graphics processor. Commands controlling the process are passed over an SMBUS that's a part of the PCI Express spec, so a graphics card that supports HybridPower is required. Unfortunately, none of Nvidia's existing graphics products support HybridPower, but the company's next-gen high-end GPUs will.

Video outputs on a high-end motherboard
Systems that use HybridPower will have their displays hooked up to the motherboard's graphics outputs. In low-power mode, discrete graphics cards will be turned off, and the chipset GPU will handle all the rendering. Switch to high-performance mode, and discrete graphics cards will come to life and assume rendering duties. However, since the system's displays will be hooked up to the motherboard, the frame buffer contents for the discrete graphics cards must be copied over to the IGP's frame buffer. According to Nvidia, second-gen PCI Express provides plenty of bandwidth for this frame buffer dump. Latency is apparently a non-issue, as well.

Video outputs on a high-end motherboard
Hybrid SLI should be a boon for gaming notebooks, allowing them to turn off power-hungry GPUs to save battery life. Nvidia is also targeting this feature for enthusiast PCs, for whom it will first become available with Nvidia's new nForce 780a chipset. The 780a's embedded GPU is capable of feeding a single digital output, be it DVI or HDMI, in addition an analog VGA output. Also packed into the 780a is a HyperTransport 3 interconnect ready to take advantage of AMD's latest Phenom processors, a full assortment of GigE, USB, and SATA ports, and 32 PCI Express 2.0 lanes via an nForce 200 chip.

The nForce 780a block diagram. Source: Nvidia
Nvidia didn't say much about the nForce 200 when the chip was first introduced, but they've now revealed a couple of additional details about the its capabilities that had previously been held back due to pending patents that have now been granted. The nForce 200 was built with SLI scaling in mind, and it includes a Posted Write Shortcut that allows data from one graphics card to be passed directly to other cards without having to loop back through the CPU. There is also a broadcast function that replicates a set of commands from the CPU across multiple graphics cards connected to the nForce 200. Both of these features are designed to reduce traffic on the 16-lane PCI Express 2.0 link that connects the nForce 200 with the 780a SPP.

Alright, enough with the nForce 200 tangent. Back to Hybrid SLI, and its slightly less exciting GeForce Boost component. In a sense, GeForce Boost describes what one might expect Hybrid SLI to be all about: harnessing the combined power of a discrete graphics card and chipset-level integrated graphics to improve performance. GeForce Boost is really designed for budget systems where discrete and integrated graphics solutions offer similar horsepower—trying to boost a mid-range or even high-end GPU's performance with a pokey IGP can actually decrease performance, Nvidia says.

Gigabyte's GeForce 8200 motherboard
The new GeForce 8200 integrated graphics chipset is Nvidia's target platform for GeForce Boost, and as one might expect, it's a budget solution aimed at Micro ATX motherboards. That's not to say Nvidia has skimped on features, though. The 8200 is fully DirectX 10-compliant and it features a PureVideo HD video engine purportedly capable of offloading 100% of the MPEG2, VC-1, and H.264 decode process for Blu-ray and HD-DVD movies. On the chipset side of things, the 8200 also features a HyperTransport 3.0 interconnect and second-generation PCI Express.
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