Page 1: Efficiency For Free: Core 2 Quad And Phenom II X4 At Reduced Voltage
Page 2:Platforms: AMD 790FX And Intel P45
Page 3:The Basics Of Undervolting
Page 4:Undervolting AMD's Phenom II X4 955
Page 5:Undervolting Intel's Core 2 Extreme QX9650
Page 6:Test Setup
Page 7: Idle/Peak Power Consumption Results
Page 8: PCMark Power And Efficiency
Page 9: Conclusion
We looked at two higher-end processors from AMD and Intel using modern MSI motherboards, to analyze the potential power savings that could be reached by undervolting the processors. Of course we intended to also undervolt the memory or the chipsets to look at additional power saving margins in those areas, but none of the motherboards we looked at allowed us to modify component voltage. These boards include the Asus P6T and Rampage II Gene, Gigabyte’s MA790FXT-UD5P and X48T-DQ6, so we stuck to MSI’s 790FX-GD70 for Socket AM3 and the P45D3 Neo for Socket LGA775.
AMD Phenom II X4: Power 17% Down, Efficiency 11.6% Up
The peak power consumption under load decreased by as much as 17% using the lowest stable voltage we found on the Phenom II X4 955. As performance didn’t change, this introduced a 11.6% increase in performance per watt using PCMark Vantage as the benchmark. AMD’s Cool’n’Quiet power saving technology poses a disadvantage for power savings through undervolting, as it always switches to its default settings regardless of your voltage configuration. Hence the idle power remained at 99 W at all times.
Intel Core 2 Extreme: Power 20% Down, Efficiency 13.8% Up
The results were even more substantial on our Core 2 Extreme QX9650 test system, where the power consumption at peak load went down by an amazing 20% without losing any performance. This allowed the performance per watt score in PCMark Vantage to improve by 13.8%. As Intel’s processor voltage in SpeedStep power saving mode depends on the set core voltage, the idle voltage decreased quite a bit as well—down to only 1.008 V. This introduced idle power savings of 8%.
Should I Do This?
We were amazed at the relatively wide margins we found for undervolting, as we had expected to run into trouble earlier. Both the AMD and the Intel machine showed that modern processors can in fact be operated at significantly reduced voltage. We achieved a 16% voltage reduction on the AMD Phenom II X4 system and 16.6% reduction on the Intel Core 2 Extreme. Both lead to system-wide power savings of 17-20% at peak.
You’ll have to be sure that your undervolt settings work reliably, but we can only recommend trying out the potential savings carefully. Keep in mind that it doesn’t have to be a 16% voltage reduction—anything around 10% should introduce major power savings at zero cost and with no performance impact.