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.

Almost 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. The exception here was the Skulltrail system, since its BIOS didn't support SpeedStep.

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 idle power consumption of Intel's 45nm processors, including the E7200 and Q9300, is impressively low.

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.

This is where the 45nm chips really come into their own. The quad-core Q9300 draws less power than the previous-gen dual-core E6750, and the E7200 is fully 30 watts below that.

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.

With their combinations of low peak and idle power, the E7200 and Q9300 use less power in total than anything else we tested. That makes some sense. The higher bins of Penryn-based products, which run at faster frequencies, are just above them.

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.

Multiple cores win the day here, since we're using a nicely multithreaded application. The Q9300's mix of low power draw and relatively strong performance nets it a third-place finish, right in the top tier along with the other Intel 45nm quad and octal solutions. The E7200 drops down the ranks some, just above the Phenom 9500.