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EPU 6-Engine
From time to time, we like to investigate Asus' EPU (energy processing unit),
a feature on its Intel motherboards that claims to reduce energy use, in large
part by adjusting the power phases of the board depending on the load state
of the system. In the past we've found that their EPU utility performs minor
tweaks like minor adjustments to CPU frequency and voltage, making it all but
impossible to determine whether the feature is actually working as it should.
On the P7H55D-M EVO, the same thing seems to apply. For example when idling
without EPU installed, CPU-Z reported a core voltage of 0.944V. With EPU installed,
calibrated and set to Auto, there was 0.024V decrease. In Medium Power Saving
mode, on load, the CPU voltage decreased by 0.16V while the CPU frequency was
slowed by 2MHz. These adjustments did very little to alter actual energy consumption,
with our instruments measuring less than a 1W difference whether measured from
the wall or at the AUX12V connector.
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EPU 6-Engine interface.
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The one good thing about the EPU feature is the ability to switch from stock
CPU settings to underclocked/undervolted at a couple of clicks of the mouse.
Putting the system in Max. Power Saving mode made our i5-661 run at 1.2GHz and
0.840V (which is basically the minimum the board's BIOS allows) regardless of
CPU load. Still, doing so only dropped the power draw during video playback
by 2~3W with no change when the system was idle.
Cooling
Lower cost boards ship with simple heatsinks on the chipset(s) while those
targeted at enthusiasts typically have large heatpipe coolers and heatsinks
on the voltage regulation modules near the CPU socket. A well-cooled motherboard
can deliver better power efficiency and stability.
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Heatsink Temperatures
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Board
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PCH
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VRMs
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Intel DH55TC
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39°C
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39~44°C (bare)
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Asus P7H55D-M EVO
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54°C
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40~45°C
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Thermalright MUX-120 with stock fan @ 5.6V (900 RPM).
Ambient temperature: 22°C.
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Cooling was not an issue on the board as the hottest point on the PCH and VRM
heatsinks measured only 54°C and 45°C respectively after 15 minutes
at full load as measured by an IR thermometer. The power draw of a dual core
i5 is not enough to justify VRM cooling though as the DH55TC with its bare MOSFETs
did not get particularly hot either.
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