Gigabyte MA785GPMT-UD2H 785G Motherboard

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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.


CPU-Z screenshot during load with default BIOS settings.


CPU-Z during load with BIOS "System Voltage Control" set to Manual.

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

Test Results: Gigabyte 785GPMT-UD2H
Test State
X3 720 BE @ 2.8GHz
(C&Q on)
X3 720 BE @ 1.6GHz (0.950V, C&Q off)
Mean
CPU
Est. System Power (DC)
Mean
CPU
Est. System Power (DC)
Idle
N/A
34W
N/A
35W
Rush Hour
(H.264)
3%
56W
2%
40W
Coral Reef
(WMV-HD)
20%
61W
24%
41W
Drag Race
(VC-1)
28%
66W
31%
44W
Disturbia
(Blu-ray H.264)
7%
62W
5%
44W
Becoming Jane
(Blu-ray VC-1)
7%
63W
6%
44W
CPU Load
N/A
108W
N/A
49W
CPU + GPU
Load
N/A
115W
N/A
58W

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.

DC Power Consumption
Test State
X3 720 BE @ 2.8GHz
(C&Q on)
X3 720 BE @ 1.6GHz (0.950V, C&Q off)
Est. System
CPU + VRM
Diff.
Est. System
CPU + VRM
Diff.
Idle
34W
15W
19W
35W
14W
21W
Rush Hour
(H.264)
56W
32W
24W
40W
17W
23W
Coral Reef
(WMV-HD)
61W
38W
23W
41W
19W
22W
Drag Race
(VC-1)
66W
42W
24W
44W
20W
24W
Disturbia
(Blu-ray H.264)
62W
35W
27W
44W
17W
27W
Becoming Jane
(Blu-ray VC-1)
63W
35W
28W
44W
17W
27W
CPU Load
108W
82W
26W
49W
28W
21W
CPU + GPU
Load
115W
83W
32W
58W
28W
30W
CPU + VRM power measured from the ATX12V connector (combined DC draw of VRMs and CPU).

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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