Power consumption and efficiency
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. And since we switch to an 890FX board for our Phenom II X6 testing, we went back and re-tested the Phenom II X4 965 on that same motherboard, to give us a direct comparison between the X4 and X6.
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 X6 1090T draws only a little more power under load than a Phenom II X4 965 on the same motherboard, and the X6's power consumption at idle isn't much higher than the X4's, either, despite the presence of two more cores and a heckuva lot more transistors. Against Intel, the competitive situation is mixed. The 1090T's power draw is comparable to that of the Core i7-920, the closest analog we have in our power tests that's based on the X58 chipset. However, the P55-based Core i7-870 draws substantially less power than the 1090T.
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.)
Relatively high power draw at idle contributes to a shaky showing for the X6 1090T here. The Core i7-920 is in the same boat, though, as are the other processors based on Intel's X58 platform. The lower-end Intel platforms, including the older Core 2 parts, fare much better.
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.
The 1090T's six cores render this scene very efficiently, finishing quickly enough to put the 1090T near the top of the standings. We don't have power data for the most directly comparable Intel parts, but the Core i7-920 is very close to the 1090T, and the i7-930 would likely be in the same ballpark.
Meanwhile, the Core i7-870 demonstrates the amazing efficiency of fully Hyper-Threaded Lynnfield processors on the P55 platform. The thing is, there's a little room for platform-level improvement on the AMD side, as well, as demonstrated by the superior efficiency of the Phenom II X4 965 when tested on an 890GX motherboard rather than the 890FX.