The video card models that will work with Hybrid SLI are fewer in number. Despite the onboard desktop chipset being the equivalent of 8th generation graphics, the 8400GS and 8500GT are the only ones out of the 8000 series lineup that are compatible. The very latest high-end cards, namely the 9800GTX/GX2 and GTX260/280, are also supported. Each card only offers compatibility with either GeForce Boost or Hybrid Power, not both. On the mobile side, all of the 9x00 generation discrete graphics are supported in at least Hybrid Power mode, with the 9200, 9300 and 9500 also offering GeForce Boost capability.
GeForce Boost is similar to previous implementations of SLI, in that it combines the processing power of two GPU's to improve 3D performance. In the past this technology involved using two individual add-in cards, and both were required to have the same GPU core. GeForce Boost works similarly, however now any of the onboard 8x00 desktop graphics can work with either of the 8x00 cards, or a combination of the 9x00 mobile series, as long as you combine two of the supported models on that platform.
Hybrid Power is designed more along the lines of 3dfx's original multi-GPU technology, the first generation Voodoo, which used separate cards for 2D and 3D applications. Unlike the Voodoo 3D daughter card, today's discrete video cards and onboard graphics are both capable of either 2D or 3D operation. Hybrid Power takes advantage of the onboard's lower power draw when in standard 2D mode, and switches on the add-in card when more demanding 3D performance is needed.
Multi Adapter Mode is a third feature not often mentioned because technically it is not part of Hybrid SLI and in fact can't be taken advantage of if either GeForce Boost or Hybrid Power is enabled. In Multi Adapter Mode, both the onboard graphics and discrete video card operate independently to support up to four displays, just as if the computer had two separate video cards. Typically many onboard graphics chips are automatically disabled when a discrete card is added, so the ability to run both simultaneously increases the functionality of the system.
One final note to keep in mind when considering Hybrid SLI is that it is only supported on Windows Vista, and only with a certain few of the latest Forceware drivers. Although we don't have any supported 9x00 mobile hardware to compare, let's take a closer look at the desktop Hybrid SLI modes.