Power consumption and efficiency
Now that we've had a look at performance in various applications, let's bring power efficiency into the picture. Our Extech 380803 power meter has the ability to log data, so we can capture power use over a span of time. The meter reads power use at the wall socket, so it incorporates power use from the entire system—the CPU, motherboard, memory, graphics solution, hard drives, and anything else plugged into the power supply unit. (We plugged the computer monitor into a separate outlet, though.) We measured how each of our test systems used power across a set time period, during which time we ran Cinebench's multithreaded rendering test.

All of the systems had their power management features (such as SpeedStep and Cool'n'Quiet) enabled during these tests via Windows Vista's "Balanced" power options profile—with a prominent exception. Our 790FX-based motherboard simply would not work with Cool'n'Quiet enabled. The system would hang shortly after the feature was enabled. As a result, we had to test the Phenoms without Cool'n'Quiet enabled. That means the Phenoms will draw more power at idle and during periods of partial load (as the rendering process starts and finishes) than they otherwise would. Power draw at peak utilization shouldn't be affected. We will try to test again with Cool'n'Quiet enabled once we get a working motherboard.

Anyhow, here are the results:

Let's slice up the data in various ways in order to better understand them. We'll start with a look at idle power, taken from the trailing edge of our test period, after all CPUs have completed the render.

The Phenom systems draw more power at idle than anything but the basket-case Quad FX system. I expect we'd see better results if Cool'n'Quiet were working properly.

Next, we can look at peak power draw by taking an average from the ten-second span from 30 to 40 seconds into our test period, during which the processors were rendering.

Under load, the Phenom systems draw about as much power as those based on Intel's 65nm quad-core processors in the 3GHz range. Unfortunately, that means the Phenom 9600 compares unfavorably to the Core 2 Quad Q6600 on power draw—and Intel isn't making things any easier with its 45nm chips. The system based on the Core 2 Extreme Q9770 at 3.2GHz draws 40W less power under load than the Phenom 9600.

Another way to gauge power efficiency is to look at total energy use over our time span. This method takes into account power use both during the render and during the idle time. We can express the result in terms of watt-seconds, also known as joules.

We can quantify efficiency even better by considering the amount of energy used to render the scene. Since the different systems completed the render at different speeds, we've isolated the render period for each system. We've then computed the amount of energy used by each system to render the scene. This method should account for both power use and, to some degree, performance, because shorter render times may lead to less energy consumption.

This final measurement shouldn't be greatly affected by the absence of Cool'n'Quiet, since it comes from the time when the CPUs are largely fully occupied. Looked at this way, the Phenom represents true progress for AMD, since systems based on dual-core chips are relatively inefficient at rendering compared to quad-core ones. But AMD has more work to do in order to catch Intel's 65nm chips, let alone its incredibly efficient 45nm ones.