Energy consumptionWe did of course use our new test protocol that allows us to measure the energy consumption of the graphics card alone. We took these reading at idle on the Windows 7 desktop as well as with the screen in standby so as to check out the impact of ZeroCore Power:
At idle, on the Windows 7 desktop, the Radeon HD 7950 consumes somewhat less energy than the Radeon HD 7970 but this is probably only due to normal variation between samples. In standby, both cards give the same performance and show an enormous improvement on all other models.
Next we measured energy consumption after several minutes in load in 3D Mark 06 and Furmark. Note that we use a version of Furmark that isn’t detected by the stress test energy consumption limitation mechanism put into place by NVIDIA in the GeForce GTX 500 drivers. We also added the readings taken in Anno 2070. Remember that by default, PowerTune limits energy consumption in scenarios that are susceptible, with the most demanding samples, to exceed 250W in the case of the Radeon HD 7970s and 200W for the Radeon HD 7950:
In 3DMark and Furmark, the Radeon HD 7970 consumes 10 to 20W more than the Radeon HD 6970, which is probably due to the more accurate estimation made by PowerTune, which kicks in for both cards both in 3DMark 06 and Furmark.
The Radeon HD 7950 is also limited by PowerTune in both these tests with a GPU clock that varies between 630 and 740 MHz in the first and between 560 and 680 MHz in the second. With the PowerTune limit raised by 20% (-> 240W), the 800 MHz clock can be maintained.
When the cards are overclocked, particularly with changes to the GPU voltage, energy consumption can go up dramatically. Here are the readings we took in Anno 2070:
800/1250 MHz @1.093V: 154W
1000/1500 MHz @1.093V: 183W
1050/1525 MHz @1.093V: 191W
1175/1525 MHz @1.225V: 272W
Lowering the GPU voltage to 0.9V does however allow you to reduce energy consumption by between +/- 30%! At 110W in Anno 2070, the Radeon HD 7950 gives a very high performance per watt ratio. We have shown this graphically, with fps per 100W to make it more legible:
The Radeon HD 7900s thus show themselves to be much more energy efficient, 55% up on the Radeon HD 6970 and almost twice as efficient as the GeForce GTX 500s! Note however that each game represents a particular case, even if Anno 2070 is sufficiently close to the average to be representative.