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Power
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 on our test system. Our results
were derived thus:
1. Power consumption of the graphics card at idle - When CPUBurn is run on a system, the video card is not stressed at all, and stays in idle mode. This is true whether the video card is integrated or an add-on PCIe 16X device. Hence, when the system power under CPUBurn with just the integrated graphics is subtracted from the system power under CPUBurn with the add-on card, we obtain the increase in idle power of the add-on card. (The actual idle power of the add-on card cannot be derived, because the integrated graphics does draw some power — we'd guess no more than a watt or two.)
2. Power consumption of the graphics card under load - The power draw
of the system is measured with the add-on video card, with CPUBurn and ATITool
running simultaneously. Then the power of the baseline system (with integrated
graphics) running just CPUBurn is subtracted. The difference is the load power
of the add-on card. (If you want to nitpick, the 1~2W power of the integrated
graphics at idle should be added to this number.) Any load on the CPU from ATITool
should not skew the results, since the CPU was running at full load in both
systems
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Power Consumption Comparison
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GPU State
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Diamond HD 4850
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ATI X1950XTX
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Asus ENGTX260
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AC
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DC (Est.)
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AC
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DC (Est.)
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AC
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DC (Est.)
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Idle
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+59W
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+50W
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+49W
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+42W
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+40W
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+35W
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Load
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+120W
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101W
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+131W
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110W
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+146W
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122W
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The ENGTX260 is clearly the most power hungry card we've tested, using up to
122W DC on full load, topping the X1950XTX's 110W and HD 4850's 101W draws.
Given these results, it's very impressive that the card can be cooled quietly
by the stock cooling unit. At idle the card draws only 35W, which is actually fairly
low for a high-end video accelerator, though more modest cards like the HD 3850/3870
use half that.
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GPU-Z screen at various states.
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To maximize power savings, the ENGTX260's GPU core and memory clock speeds
vary depending on the type of load the system is under. According to GPU-Z,
the card clocks itself to 300/100Mhz when idle, 400/300Mhz when video playback
is initiated, and 576/999Mhz when the GPU is stressed with 3D applications.
Video Playback
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Video Playback Results
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Video Clip
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Mean CPU Usage
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Peak CPU Usage
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AC Power
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Rush Hour
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2%
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7%
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~131W
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Coral Reef
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15%
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25%
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~139W
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Flight Sim.
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30%
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48%
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~151W
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Drag Race
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33%
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44%
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~153W
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As expected, the ENGTX260 handled our video playback tests
with ease. CPU usage during playback was very low, and never peaked past 50%.
Power consumption varied greatly depending on the type of clip being played
with the most stressful VC-1 clips elliciting about 20W more than the Rush Hour
H.264 clip.
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Video Playback Comparison
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Video Clip
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Diamond HD 4850
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Asus ENGTX260
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Asus EN9600GT
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Mean CPU
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AC Power
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Mean CPU
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AC Power
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Mean CPU
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AC Power
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Rush Hour
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3%
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~136W
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2%
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~131W
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2%
|
~113W
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Coral Reef
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28%
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~151W
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15%
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~139W
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15%
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~121W
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Flight Sim.
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55%
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~168W
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30%
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~151W
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28%
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~131W
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As the card is equiped with the same (and as far as we know, unchanged) PureVideo
HD decoder as the previous nVidia-based card we tested, the EN9600GT, the CPU
usage results were very similar. And while it plays video more efficiently than
the HD 4850, the EN9600GT is even more frugal. Generally speaking, the more
advanced the graphics card is, the more power it consumes when idle — and
this usually applies to video playback as well. Obviously if video playback
is the card's main task, a much cheaper, low power card can do just as well.
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