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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.

Anyhow, here are the results:

If you're like me, you looked at that raw data on the QX9650 and immediately did a double-take. It's for real, though.

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.

Surprisingly, our QX9650 system draws substantially less power—34W, to be exact—at idle than the otherwise-identical QX6850 system did. That drops the QX9650 power consumption even below that of the dual-core Core 2 Duo E6750.

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.

The 45nm chip's reduction in power use under load is even more impressive. The QX9650 system pulls 74W less under load than the QX6850-based one—less than an Athlon 64 X2 5600+, astoundingly enough.

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.

Obviously, with such low idle and peak power consumption, and its quick render time, the QX9650 doesn't draw much power during the duration of our test period.

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.

The Core 2 Extreme QX9650 combines some of the lowest power consumption of the group with the quickest render times. That means it's able to render the scene with under half the energy used by the Core 2 Duo E6750. Compared to the 65nm Core 2 Extreme QX6850 running at the same clock speed, the QX9650 brings a 33% reduction in system-level energy use during this task.