Power consumption and efficiency
We have reams of test results to wade though, but we'll begin with our power consumption tests, since they're especially relevant to a new 32-nm processor like the Core i7-980X.
For these tests, we used an Extech 380803 power meter to 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 systemthe CPU, motherboard, memory, graphics solution, hard drives, and anything else plugged into the power supply unit. (The monitor was plugged into a separate outlet.) 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.
We'll start with the show-your-work stuff, plots of the raw power consumption readings. We've broken things down by socket type in order to keep them manageable. Please note that, because our Asus H57 motherboard tends to draw more power than we'd like, we've tested power consumption for the Core i5-530 and the Core i5-661 on our P55 mobo, instead.
We can slice up these raw 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.
Next, we can look at peak power draw by taking an average from the ten-second span from 15 to 25 seconds into our test period, when the processors were rendering.
The Core i7-980X's power draw, both at max and idle, mirrors that of the Core i7-975 quite closely. Heck, it's a few watts lower at peak, despite the addition of two more cores and extra cache.
We can highlight power efficiency by looking 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. (In this case, to keep things manageable, we're using kilojoules.)
The X58 platform's relatively high power use at idle keeps the i7-980X from performing well by this measure.
We can pinpoint efficiency more effectively by considering the amount of energy used for the task. 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.
In our most direct measurement of power efficiency, the Core i7-980X takes top honors. With six cores and, thanks to Hyper-Threading, 12 hardware threads, the 980X makes short work of Cinebench's test render. By finishing so quickly, the 980X-based system requires the least energy to render this scene. Holding the line on clock speeds and raising the core count is a very effective strategy for attaining energy-efficient performance in multi-threaded applications, and Intel has followed that template almost perfectly with Gulftown.
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