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HybridPower in action
Our initial nForce 780a SLI testing was conducted with a GeForce 8800 GT graphics card that isn't compatible with Hybrid SLI. To test Hybrid SLI—more specifically, its HybridPower component—we swapped in a GeForce 9800 GTX with HybridPower-aware ForceWare 174.14 drivers.

Before jumping into some benchmark results, I should spend a moment explaining how HybridPower works from a user perspective. Or at least how it's supposed to work. HybridPower actually consists of three modes: save power, boost performance, and additional displays. The first two are self-explanatory, and Windows is supposed to switch between them automatically based on the system load. Automatic mode switching didn't work right on our system, though, regardless of which Vista power plan we tried. I suspect the combination of beta graphics drivers and the fact that we previously had a GeForce 8800 GT with an older graphics driver revision installed might have gummed things up, but who knows.

Fortunately, HybridPower has a provision for manual mode switching via a handy taskbar icon, and that worked just fine. Switching between modes is flicker-free and only takes a couple of seconds with an empty desktop. However, the more windows you have open, the longer it will take to switch modes. Also, you can't switch modes if an open application is using the 3D subsystem. That might not seem like much of a hindrance—you aren't likely to switch modes while playing games—but many desktop apps make use of a graphics card's 3D horsepower. Paint Shop Pro Photo X2, for example, can't be open if you want to switch HybridPower modes. Vista's Aero interface isn't a problem, though.

Another minor annoyance related to mode switching is its propensity to center the mouse pointer. This is a minor problem at best, and one that Nvidia should be able to rectify.

If you're not interested in HybridPower's energy-saving potential, an "additional displays" option allows the motherboard's display outputs to be used in conjunction with those of a discrete graphics card to power multiple displays. This isn't a particularly new capability for integrated graphics, but it is a separate option that effectively disables power saving mode.

So what kind of impact does HybridPower have on system performance and power consumption? We whipped up a quick batch of benchmarks to find out. Performance tests were run with HybridPower in boost performance mode to gauge the impact of frame buffer replication to the motherboard GPU.

HybridPower slows our system down by a hair, but that's about it. All in all, not bad for a first attempt, especially when you consider the potential for power savings.

Our idle power consumption tests were run in power-saving mode, and the results speak for themselves. With a GeForce 9800 GTX, HybridPower saves a whopping 57W. Impressive.

Under load, where we tested with HybridPower in boost performance mode, power consumption is actually higher. I suspect at least some of the extra power draw can be traced to the additional processing required for frame buffer replication. Also, the 780a's motherboard GPU slips into a low-power state when HybridPower is disabled, reducing its power consumption.