Power Consumption
Sandy Bridge-E isn’t on the same tick-tock cadence as Intel’s desktop processors. We’re a few months away from the next “tick,” in the form of Ivy Bridge, and here we are evaluating the performance of a “tock”-derivative.
That’s not bad news by any stretch of the imagination. Intel nailed its 32 nm lithography node, giving the company a mature process on which to build this 2.27 billion-transistor, 434 square-millimeter processor. Gulftown, in comparison, is comprised of 1.17 billion transistors in a 248 mm2 die. Despite that disparity in size and composition, Intel manages to work Sandy Bridge-E into a 130 W TDP, just like the Core i7-990X.
| Processor | Idle System Power Consumption |
|---|---|
| Intel Core i7-3960X (Sandy Bridge-E) | 87 W |
| Intel Core i5-2500K (Sandy Bridge) | 90 W |
| Intel Core i7-2600K (Sandy Bridge) | 90 W |
| AMD Phenom II X4 980 (Deneb) | 100 W |
| AMD FX-8150 (Zambezi) | 111 W |
| AMD Phenom II X6 1100T (Thuban) | 114 W |
| Intel Core i7-990X (Gulftown) | 127 W |
| Intel Core i7-920 (Bloomfield) | 130 W |
And yet, at idle, Core i7-3960X behaves a lot like a 95 W Sandy Bridge desktop processor, dropping down to less than 90 W of system power use measured after 10 minutes of sitting on the Windows desktop. In comparison, Bloomfield (Core i7-920) and Gulftown (Core i7-990X) are much more power-hungry at idle.
After measuring idle system power use, I ran and logged complete runs of PCMark 7 to track average power use in a more graphically-representative way. In order to keep the chart from getting too muddled, I only left Core i7-3960X, Core i7-990X, and FX-8150. You can see, though, in looking at the peaks and dips, that Sandy Bridge-E is using less power than either of its competitors.
Averaging system power use gives us this list:
| PCMark 7 System Power Consumption, Logged In Two-Second Intervals | |
|---|---|
| Processor | Average Power Across One Run |
| Intel Core i5-2500K (Sandy Bridge) | 153 W |
| Intel Core i7-2600K (Sandy Bridge) | 155 W |
| Intel Core i7-3960X (Sandy Bridge-E) | 172 W |
| AMD Phenom II X4 980 (Deneb) | 184 W |
| Intel Core i7-990X (Gulftown) | 189 W |
| AMD Phenom II X6 1100T (Thuban) | 191 W |
| AMD FX-8150 (Zambezi) | 191 W |
| Intel Core i7-920 (Bloomfield) | 193 W |
Core i7-3960X indeed uses less power, on average, than the 130 W Gulftown- and Bloomfield-based parts. It’s bested only by Intel’s 95 W Sandy Bridge processors. Even AMD’s older Phenom II X4 and X6 chips are more power-hungry (as is FX-8150).
| Prime95 x64 Small FFTs System Power Consumption | |
|---|---|
| Processor | Power Consumption After 5 Minutes |
| Intel Core i7-2600K (Sandy Bridge) | 175 W |
| AMD Phenom II X4 980 (Deneb) | 221 W |
| AMD Phenom II X6 1100T (Thuban) | 230 W |
| Intel Core i7-3960X (Sandy Bridge-E) | 253 W |
| Intel Core i7-990X (Gulftown) | 263 W |
| AMD FX-8150 (Zambezi) | 264 W |
Of course, PCMark 7 doesn’t push processors to their limit. For that, we turn to Prime95, which I didn’t run in our FX-8150 review, but include here with most of the platforms in that story re-tested.
Core i7-3960X on Intel’s DX79SI board cuts peak power consumption by 10 W compared to Core i7-990X on Asus’ Rampage III Formula, which itself uses 1 W less than AMD’s FX-8150 on Asus’ Crosshair V Formula.
Core i7-2600K is the only CPU able to facilitate a less-than-200 W system power number, dipping in at 46 W less than the second-place finisher, AMD’s Phenom II X4 980 Black Edition.
Surprised at the savings, especially compared to the smaller and less complex Gulftown design, I asked Intel to help explain how Sandy Bridge-E could possibly use less power. The response was that two cores in the 2.27-billion transistor die are completely fused off, and that a number of other power/speed path improvements were made to help cut the CPU’s draw.