Total System Power Consumption
Before bringing this article to a close, we'd like to cover a few final data points--namely power consumption and noise. Throughout all of our benchmarking and testing, we monitored how much power our test system was consuming using a power meter. Our goal was to give you all an idea as to how much power each configuration used while idling and while under a heavy workload. Please keep in mind that we were testing total system power consumption at the outlet here, not just the power being drawn by the graphics cards alone.
With what are basically two Radeon HD 6970 cards crammed onto a single PCB, we expected the Radeon HD 6990's power consumption to be relatively high in comparison to virtually all other high-end, current-gen graphics cards and that was in fact the case. Idle power consumption is fairly good; the Radeon HD 6990 actually consumes less than 20 watts more than the Radeon HD 6970 and less than 10 watts more than the GeForce GTX 580. Under load conditions, however, the Radeon HD 6990's power consumption spikes way up and the card uses about 100 to 150 additional watts over a GeForce GTX 580, depending on the 6990's configuration.
At power consumption levels this high, it should come as no surprise that the Radeon HD 6990 can get somewhat noisy under load. Temperatures, however, are kept in check thanks to some large heatsinks and a fan speed profile that gets air moving rather quickly, once temperatures ramp up.
Under load, the Radeon HD 6990 will definitely be audible over the noise a typical high-end PC generates from its cooling fans, drives, etc. We would not call the card excessively loud, however. Once the fan spins up above the 45% mark or so, its volume easily drowned out the other fans in our test bed, but the pitch of the fan wasn't annoying. It's probably in the same class as a pair of Radeon HD 5870 cards, perhaps just a bit louder.
As for temperatures, though, the AMD's fairly aggressive fan speed profile helps keep them manageable. We witnessed GPU temperatures in the mid-80'C range and watched the fan speed fluctuate from about 39% to 45%, which easily pulled the GPU temps back down closer to 80'C. While idle, the card didn't pump out very much heat at all and the fan is barely audible.