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 big exception here, of course, is Skulltrail, since its pre-release BIOS doesn'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.

Even without SpeedStep to dial the clock speed and voltage back at idle, the Skulltrail system draws considerably less power than the older dual Xeon rig, and it's right in line with AMD's Quad FX system.

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.

Skulltrail's peak power draw of about 370W is surprisingly tame, all things considered. This is a nice improvement over the Xeon X5365s, even if it's not exactly sipping power.

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.

All told, this eight-core system only uses slightly more energy during our test period than our Athlon 64 X2 6000+-based test rig.

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.

Here's the multicore system's ace in the hole. Because it finishes the rendering work so quickly, Skulltrail requires less total energy than all but one of our other test systems.