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CPU Voltage
Before we get to our primary test results, we need to inform our readers of
an odd anomaly we encountered on the 785GPMT. Our initial tests revealed unusually
high power consumption when the CPU was placed on load, about 20~30W more than
the previous 785G mainboards we tested when measured from the wall. It turns
out the the board applied more CPU voltage than normal for our X3 720 processor.
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CPU-Z screenshot during load with default BIOS settings.
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CPU-Z during load with BIOS "System Voltage Control" set to
Manual.
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In the BIOS, there is a setting called "System Voltage Control" which
can be set to Auto or Manual. All it really does is toggle the ability to adjust
the various voltages, CPU, chipset, memory, etc. Strangely, when it was set
to Auto, it caused the board to deliver the equivalent of a 1.400V manual setting
to the CPU, even though the BIOS reported that it was running at 1.325V. Changing
the setting to Manual solved the problem, even though we did not actually enter
in a specified CPU voltage. This is something to watch out for as systems based
on the 785GPMT-UD2H left at stock settings could easily suck down 30W or more
than is necessary.
Test Results
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Test Results: Gigabyte 785GPMT-UD2H
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Test State
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X3 720 BE @ 2.8GHz
(C&Q on)
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X3 720 BE @ 1.6GHz (0.950V, C&Q off)
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Mean
CPU
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Est. System Power (DC)
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Mean
CPU
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Est. System Power (DC)
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Idle
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N/A
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34W
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N/A
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35W
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Rush Hour
(H.264)
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3%
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56W
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2%
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40W
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Coral Reef
(WMV-HD)
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20%
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61W
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24%
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41W
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Drag Race
(VC-1)
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28%
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66W
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31%
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44W
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Disturbia
(Blu-ray H.264)
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7%
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62W
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5%
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44W
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Becoming Jane
(Blu-ray VC-1)
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7%
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63W
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6%
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44W
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CPU Load
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N/A
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108W
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N/A
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49W
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CPU + GPU
Load
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N/A
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115W
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N/A
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58W
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Like the previous 785G boards, the 785GPMT blew through our video playback
test suite without any difficulties. "Becoming Jane," a VC-1 Blu-ray
recently added to our test suite played with very little CPU usage, similar
to our H.264 Blu-ray and H.264 Quicktime trailer.
When we underclocked the processor to 1.6GHz and used as little voltage as
possible while maintaining stability (0.950V), we noticed that CPU activity
remained almost constant during video playback, making it clear that the GPU
did indeed do all the heavy lifting in the decoding process. System power consumption
in this undervolted/underclocked state lowered by 16~22W during playback.
DC Power Consumption
Since our last motherboard review, we've begun measuring the power draw directly
from the ATX12V connector which gives us the combined energy demand of the CPU
and VRMs. Subtracting this figure from the estimated system DC power draw gives
us a good idea of how much the other components actually use, once you take
the CPU and VRMs out of the picture.
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DC Power Consumption
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Test State
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X3 720 BE @ 2.8GHz
(C&Q on)
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X3 720 BE @ 1.6GHz (0.950V, C&Q off)
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Est. System
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CPU + VRM
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Diff.
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Est. System
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CPU + VRM
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Diff.
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Idle
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34W
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15W
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19W
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35W
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14W
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21W
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Rush Hour
(H.264)
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56W
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32W
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24W
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40W
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17W
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23W
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Coral Reef
(WMV-HD)
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61W
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38W
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23W
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41W
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19W
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22W
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Drag Race
(VC-1)
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66W
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42W
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24W
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44W
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20W
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24W
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Disturbia
(Blu-ray H.264)
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62W
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35W
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27W
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44W
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17W
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27W
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Becoming Jane
(Blu-ray VC-1)
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63W
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35W
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28W
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44W
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17W
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27W
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CPU Load
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108W
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82W
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26W
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49W
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28W
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21W
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CPU + GPU
Load
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115W
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83W
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32W
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58W
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28W
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30W
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CPU + VRM power measured from the ATX12V connector
(combined DC draw of VRMs and CPU).
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At stock settings, the motherboard, two sticks of memory, notebook hard drive,
idle Blu-ray drive, mouse and keyboard use between 19W and 32W DC depending
on the load. In our undervolted/underclocked state, it was between 21W and 30W
DC.
On a side note, on full load, our Phenom II X3 720 (95W TDP) draws somewhere
around 82W, with a small, but indeterminate amount lost to VRM inefficiency.
[Editor's Note: VRM efficiency in motherboards can vary quite
a bit, from <75% in el cheapo consumer boards to >90% in high end server/workstation
boards. VRM efficiency has risen in general over the past few years, due to
improvements in components and the green-motivated push to reduce energy consumption.
With DC/DC conversion such as the VRMs, it's reasonably safe to assume ~85%
efficiency or better these days.]
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