Power Consumption

Cooling modern video cards is becoming more and more difficult, especially when users are asking for quiet cooling solutions. That's why the engineers are now paying much more attention to power consumption of new video card designs.


In order to characterize a video card's power consumption, the whole system's mains power draw was measured. This means that these numbers include CPU, Memory, HDD, Video card and PSU inefficiency.

The three result values are as following:

• Idle: Windows sitting at the desktop (1024x768 32-bit) all windows closed, drivers installed.
• Average: 3DMark03 Nature at 1280x1024, 6xAA, 16xAF. This results in the highest power consumption. Average of all readings (two per second) while the test was rendering (no title screen).
• Peak: 3DMark03 Nature at 1280x1024, 6xAA, 16xAF. This results in the highest power consumption. Highest single reading

In idle the power consumption of the HD 4870 X2 is essentially the same as the single-GPU HD 4870. While this alone is a good achievement, the card's idle power consumption is still much higher than that of similar performing offerings from NVIDIA (GTX 280).

The power hungry HD 4870 X2 easily claims the number 1 (or "last") spots when it comes to load and peak power consumption. Especially the peak power consumption reaches new levels never seen before.

In order to keep the power consumption down of their card AMD has implemented R600 style 2D/3D clocks in their card - the dynamic power management of the RV770 is not used at all.
On the HD 4850 and HD 4870 the GPU is configured in a way to dynamically adjust the clock frequencies based on GPU load, without any software intervention - this is disabled now. Instead the driver detects if the card is running in 2D or fullscreen (!) 3D and switches clocks accordingly. In 2D and windowed 3D the card will always run at 500 MHz / 500 MHz to conserve power. Also it seems CrossFire is disabled when running windowed 3D apps. I did a quick test with Crysis (same settings for both tests) and got 27.1 FPS in a window and 54.4 FPS in fullscreen 3D, quite a difference.