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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. 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 power consumption of the base system under CPUBurn 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 (Intel GMA950). (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 FurMark
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 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.
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Power Consumption Comparison (DC)
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Card
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Est. Power (Idle)
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Est. Power (ATITool)
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Est. Power (FurMark)
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ATI HD 4830*
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18W
|
80W
|
87W
|
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Diamond HD 4850
|
50W
|
101W
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N/A
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Asus ENGTX260
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35W
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122W
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N/A
|
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ATI HD 4870 1GB
|
67W
|
121W
|
134W
|
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Asus HD 4870 512MB Matrix**
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48W
|
128W
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140W
|
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* sample with unknown number of stream processors
** average idle power used
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Even though ATI's card had an extra 512MB to power, the overclocked Asus Matrix drew an extra 6-7W DC on a full load. On the bright side, idle power
was actually lower by almost 20W — the Power Saving mode
during 2D use pays off.
BIOS
The Matrix card had a nifty utility to display the card's operating
voltages and frequencies. The ATI card had no such application, so to get a
better idea of its inner workings we took a look at the board's BIOS. We used
GPU-Z to extract the card's BIOS and Radeon
BIOS Editor to examine how the card's clock speeds and voltages were set
to behave.
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ATI HD 4870 1GB: BIOS Clock/voltage settings.
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Displayed in green, yellow and red are the card's settings for idle, UVD, and
3D. We confirmed the frequency changes with GPU-Z, but the BIOS shows us a voltage
jump of 0.060V when the 4870 1GB enters 3D mode.
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ATI HD 4870 1GB: BIOS Fan settings.
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The fan control behavior follows a simple linear progression starting at a
GPU temperature of 58°C and finishing at 101°C.
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Asus HD 4870 512MB Matrix: BIOS Clock/voltage settings.
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The Matrix's BIOS shows the voltages locked at 1.263V — you're expected
to use iTracker if you want any power savings. The fan control panel was greyed
out, so we still have no insight into the how the card's main fan operates.
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