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The power consumption of an add-on video card can be estimated by comparing the total system power draw with and without the card installed. Our results were derived thus:
1. Power consumption of the graphics card at idle when Prime95 is run on a system, the video card is not stressed at all and stays idle. This is true whether the video card is integrated or an add-on PCIe 16X device. Hence, when the power consumption of the base system under Prime95 is subtracted from the power consumption of the same test with the graphics card installed, we obtain the increase in idle power of the add-on card over the integrated graphics chip.
2. Power consumption of the graphics card under load the power draw of the system is measured with the add-on video card, with Prime95 and FurMark running simultaneously. Then the power of the baseline system (with integrated graphics) running just Prime95 is subtracted. The difference is the load power of the add-on card. Any load on the CPU from FurMark should not skew the results, since the CPU was running at full load in both systems.
Both results are scaled by the efficiency of the power supply (tested here) to obtain a final estimate of the DC power consumption.
Note: the actual power of the add-on card cannot be derived using this method because the integrated graphics may draw some power even when not in use. However, the relative difference between the cards should be accurate.
According to our calculations, the HD 7870 DirectCU II consumed about 14W when idle and 189W on full synthetic load. Its load draw is very close to the HD 6870 but it uses almost half as much energy when idle. It's supposed to be a much faster card though, so these figures are fairly impressive.
Like many previous high-end Radeon graphics cards, playing hardware-accelerated HD video wasn't nearly as efficient. Measured from the wall, our HD 7870-equipped GPU test system consumed 83W when playing high definition H.264 and Flash video compared to 50W when idle. The culprit seemed to be high clock speeds when the HD 7870's UVD chip was activated, a common issue we've had with past AMD video cards. According to GPU-Z, its core/memory speeds were 450/1250 MHz compared to 300/150 MHz when idle.
All of the AMD/NVIDIA cards from the last three generations had very similar CPU usage during video playback, 1~2% for our 1080p H.264/MKV test clip, and 8~9% for our YouTube HD sample the 7870 was no exception.
MP3 Sound Recording
This recording was made with a high
resolution, lab quality, digital recording system inside SPCR's
own 11 dBA ambient anechoic chamber, then converted to LAME 128kbps
encoded MP3s. It's intended to give you an idea of how our test system sounds
in actual use one meter is a reasonable typical distance between a computer
or computer component and your ear. The recording contains stretches of ambient
noise that you can use to judge the relative loudness of the subject. Be aware
that very quiet subjects may not be audible if we couldn't hear it from
one meter, chances are we couldn't record it either!
The recording starts with 5~10 seconds of room ambiance, followed by 5~10 seconds
of the GPU test system with its case fans at various speeds. For the most realistic results, set the volume
so that the starting ambient level is just barely audible, then don't change
the volume setting again.
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