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 dual Opteron 252, four for the Pentium XE 840, two for the Opteron 175, 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 or PowerNow. (In the case of the Pentium 4 600-series processors, the C1E halt state is always available, even in the "no power management" tests.) Sadly, the beta BIOS we used for our Tyan S2895 motherboard didn't support AMD's PowerNow, so we couldn't report scores for the Opterons with power management enabled.

At idle and under load, AMD appears to have delivered on its promise: the dual-core Opteron 175 actually consumes less power than the Opteron 152. Since power consumption is pretty directly related to heat output, AMD appears to have hit both its power and heat targets for the dual-core parts. Even the quad-core Opteron 275 system consumes substantially less power under load than the dual Xeon rig or the Pentium XE 840.

Incidentally, simply by turning off Hyper-Threading, the Pentium XE's power consumption under load drops from 313W to 292W.

Here's something kind of interesting. Since we're dealing with dual-socket systems, we can calculate the power consumption delta when going from single to dual CPUs. That lets us isolate CPU power consumption from overall system consumption—at least in theory, I think, and don't sue me please.

Again, the Opteron 175 is well within the power envelope established by its predecessors.