Power consumption
We measured the power consumption of our entire test systems, except for the monitor, at the wall outlet using a Watts Up PRO watt meter. The test rigs were all equipped with OCZ PowerStream 520W power supply units. The idle results were measured at the Windows desktop, and we used SMPOV and the 64-bit version of the POV-Ray renderer to load up the CPUs. In all cases, we asked SMPOV to use the same number of threads as there were CPU front ends in Task Manager—so four for the Pentium XE 840, two for the Athlon 64 X2, and so on.

The graphs below have results for "power management" and "no power management." That deserves some explanation. By "power management," we mean SpeedStep, PowerNow!, or Cool'n'Quiet. In the cases of the Pentium XE 840 and the Pentium XE 965, the C1E halt state is always active, even in the "no power management" tests. The Extreme Edition 955 and the P4 Extreme Edition 3.73GHz don't support the C1E halt state or SpeedStep. We have omitted the Pentium D 930 and 950 processors here because we don't have actual samples of these individual chips; our "simulated" versions with an underclocked Extreme Edition 955 are fine for performance testing, but not for power consumption.

In spite of its higher clock speed, the Extreme Edition 965 draws much less power than the 955. That's impressive. Of course, these are power consumption numbers at the wall socket, so various inefficiencies in the system power supply chain will inflate the differences between the chips to some degree. But over 50W less power use under load for the 965 XE is a noteworthy result, regardless. At idle, the C1E halt state on the 965 kicks in, lowering power draw there compared to the 955 XE.

Notice that we also have numbers for the 955 XE on a "new mobo." You may have noted in our testing methods section that we tested the Extreme Edition 965 on a newer revision of Intel's "Bad Axe" D975XBX motherboard. We received the new motherboard during our efforts to resolve some overheating problems with our original 955 XE setup. I wanted to be sure the motherboard wasn't the main cause of the power consumption differences between the 955 and 965 processors, so I tested the 955 on the newer-rev motherboard, as well. As you can see, the motherboard did play a partial role in the power use difference under load, but not at idle.

The most eyebrow-raising result of all here is that the Extreme Edition 965 system consumes no more power under load than the Athlon 64 FX-60 system. That's huge. I would be more impressed were it not for the relatively high power consumption of the Asus A8N32-SLI motherboard and the nForce4 SLI X16 chipset. The AMD processors can post lower numbers on a different motherboard like the Asus A8R32-MVP. I note that issue because it's only fair, not to take away from Intel's accomplishment here, which is still eye-popping. Obviously, Intel's 65nm fabrication process is improving with time.

I should mention, however, that the cooler Intel shipped with our Extreme Edition 965 review sample was very loud under load, just like the replacement cooler we eventually used to help resolve our thermal problems with the 955 XE. It's not exactly whisper-quiet at idle, and when you fire off a program that heats up the chip, the cooler spins up linearly in a whining, hissing crescendo. You will almost certainly want to go with an aftermarket cooler with this CPU if this cooler is representative of what Intel is shipping with retail boxed processors.