PC Perspective Advanced Power Testing

For our power consumption tests on new GPUs, we previewed a new measurement method last year that we are finally taking advantage of. This isn’t an “at the wall” measurement with a Watts Up or something similar to that; instead we are measuring power directly from the graphics card itself.

How do we do it? Simple in theory but surprisingly difficult in practice, we are intercepting the power being sent through the PCI Express bus as well as the ATX power connectors before they go to the graphics card and are directly measuring power draw with a 10 kHz DAQ (data acquisition) device. A huge thanks goes to Allyn for getting the setup up and running. We built a PCI Express bridge that is tapped to measure both 12v and 3.3v power and built some Corsair power cables that measure the 12v coming through those as well.

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The GeForce GTX 1070, GTX 970 and Radeon R9 Nano are well within reach of each when it comes to total power draw, but that yellow line representing the Radeon R9 390X and its 275 watt TDP is…higher. Clearly the Tahiti GPU is showing its age and its inability to compete with even AMD’s on Hawaii GPU in terms of power efficiency, and it definitely isn’t competing with the likes of the GTX 1070.

Another interesting data point from these results is in the comparison of the GTX 1070 and GTX 970. Even though the GTX 1070 is rated at 5 watts HIGHER than the GTX 970, our result show it actually uses less power (in our two tested games at least) than the Maxwell-based GM204 part.

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Looking at only the NVIDIA products in our power testing scenarios, the GTX 980 Ti is the biggest draw here, as expected, with a 250 watt TDP.

Now that we are have direct power measurement numbers to use, rather than power from the wall results that could be tainted by increased CPU usage at any of these points, we can do some interesting performance per watt measurements for all parties involved.

Clearly the new 16nm GP104 is the most power efficient GPU we have ever tested, and the results above with the GTX 1070 compared to Maxwell, Hawaii and Tahiti prove that out. 

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