The AM2 Athlon64 X2 5000+ draws more power than the mPGA939 Athlon64 FX-60, yet while both chips are clocked at the 2.6GHz the X2 5000+ has less cache... The difference in power consumption could be chalked up to the different motherboard and memory infrastructures; one platform is DDR, the other DDR-2.

Total System Idle Power Draw
Processor	Total System Power Draw
Intel Pentium 4 540	150 Watts
Intel Pentium D 840	165 Watts
Intel Pentium D 940	168 Watts
AMD Athlon64 4000+	163 Watts
AMD Athlon64 FX-60	127 Watts
AMD Athlon64 X2 5000+	156 Watts
AMD Athlon64 FX-62	168 Watts

The AM2 Athlon64 FX-62 system chews up a bit more power (168W) than the X2 5000+ at idle (156W), which is not unexpected. The Intel Pentium D 940 and 840 systems draw upwards of 168/165W at idle, equivalent to the AM2 FX-62. The 2.4GHz Athlon64 4000+ is built on the larger 0.13 micron manufacturing process, so we're not surprised to find it's system consumes 163W in this test.

Power consumption with processors under load will be much higher, and this separates the more power efficient systems from those that are more power conservative.

Total System Stressed Power Draw
Processor	Total System Power Draw
Intel Pentium 4 540	223 Watts
Intel Pentium D 840 (Single Core Load)	203 Watts
Intel Pentium D 840 (Dual Core Load)	240 Watts
Intel Pentium D 940 (Single Core Load)	230 Watts
Intel Pentium D 940 (Dual Core Load)	253 Watts
AMD Athlon64 4000+	172 Watts
AMD Athlon64 FX-60 (Single Core Load)	163 Watts
AMD Athlon64 FX-60 (Dual Core Load)	196 Watts
AMD Athlon64 X2 5000+ (Single Core Load)	177 Watts
AMD Athlon64 X2 5000+ (Dual Core Load)	207 Watts
AMD Athlon64 FX-62 (Single Core Load)	196 Watts
AMD Athlon64 FX-62 (Dual Core Load)	235 Watts

Total system power draw rises to 253W when both cores of the Intel Pentium D 940 processor are under load. If we change how the system is stressed and only task a single core, the Pentium D 940's power consumption isn't impacted all that much. In fact the meter on the Extech Power Analyzer drops just 23W. On the flip side, under the same dual core conditions the AMD Athlon64 FX-62 system draws 235W, not much better there.

The socket AM2 Athlon64 X2 5000+ system on the other hand draws 207W with both cores stressed, and 177W otherwise.

Of the two socket AM2 processors we're testing in this review, the AM2 Athlon64 X2 5000+ will be the more energy efficient model in the long run. A new metric called performance-per-watt is emerging as a means of weighing the benefits of desktop PC performance potentials. Pay close attention to the benchmarks, and consider the performance per watt of each candidate CPU. Power reductions on this small scale will not translate into much for the average user, but businesses that require always-on hardware will surely be interested in the cost savings these little power reductions add up to.