Undervolting Your Phenom II And Core 2 Processors

Efficiency For Free: Core 2 Quad And Phenom II X4 At Reduced Voltage

Enthusiasts generally try staying up to date when it comes to overclocking processors. They spend a lot of time answering these sorts of questions: How fast can certain processors go? What voltage levels do you need to get there? And what’s the best cooling solution?

But while overclocking lets you bump CPU performance to the levels of more expensive processor models, it is also possible to go in the other direction. You can typically undervolt a processor in an effort to improve efficiency without affecting performance at all.

Voltage, Clock Speed, and Power Consumption

Clock speed is one of the biggest determinants of performance, and increasing voltage is typically an action taken to enable higher clock speeds. With that said, voltage plays the most important role in establishing power consumption, with clock speed playing a secondary role in that arena. Increasing or decreasing clock speeds has a straight proportional impact on power, while power actually scales with the square of voltage. For this reason, bumping up voltage always has a more significant impact on power consumption than a clock speed increase.

And of course, reducing the operating voltage can have a significant impact on power consumption, which is why we decided to look into it.

Lower Voltage Products

Many mobile processors are simply modified, low-voltage versions of common products. Think of Intel’s Core 2 mobile processors. These are power-optimized, but under comparable conditions, they would perform and consume power like their desktop brothers. The Core 2 Duo T-series is rated at a maximum power consumption of 35 W, the P-series stays within a 25 W envelope, and so forth.

But there are low-power parts for desktop systems as well. AMD offers energy efficient processors with the suffix “e” (Phenom II X4 900e, 905e, and the Phenom X4 9350e). Intel is offering Core 2 Quad “S” models, which deliver the same performance as the regular models, but within a 65 W thermal envelope instead of 95 W. Although the lower-power processors are too expensive, if you ask us, they don’t fail to impress, as both the idle and peak power of test systems decreases.

Low-Voltage CPU Do-It-Yourself?

So what if we were to tweak CPU voltage ourselves? If overclocking and overvolting have become so popular, it couldn’t hurt to try some undervolting. We setup two MSI motherboards that we had at our disposal: a P45D3 Neo, which we recently used to find the perfect Core 2 Duo overclock, but this time with a Core 2 Extreme QX9650, and a 790FX-GD70, allowing us to test AMD’s Phenom II X4 955.