Test Results: Idle, Continued
Phenom II X3 710
Without power management, the same system sporting a 100 MHz-slower Phenom II X3 710 (three cores and a larger 6MB L3 cache) consumes about the same amount of power at idle as an Athlon X2 7750. Enable the revised Cool'n'Quiet, though, and you'll see power consumption drop another 10 watts. Now go for broke and tweak the voltages. You can hit very low levels of power consumption--well below 60 watts.
Enabling power management saves around 13 watts, but tweaking the voltages really pushes the envelope further, saving an additional 12 watts or a total of 25 watts compared to running without power management. In percentages, that's 30% less power.
Phenom II X4 945
The Phenom II X4 945's actual power consumption may be lower than what we’re seeing here. When we ran the Athlon X2 7750 on this board, the result was noticeably higher than with the Biostar's TA790GX 128M--about 10 watts higher at idle. The GA-MA790GP-DS4H also applied a fairly high voltage for the Phenom II X4 945 (1.35V for the core and 1.1V for the northbridge).
Running at 3 GHz with all four cores functional and a full complement of 6MB L3 cache, the system with AMD's Phenom II X4 945 consumes about 100 watts at idle. Enable Cool'n'Quiet and select the “Balanced” policy; power consumption drops to around 77 watts. Lower operating voltages and you drop an additional 7 watts. In percentages, we've just saved about 30%. We believe that, with a more frugal motherboard, we could probably save more.
Phenom II X4 955
With a slightly higher clock rate, the Phenom II X4 955's actual power consumption is slightly higher than the Phenom II X4 945. Thankfully, power consumption levels with Cool'n'Quiet are about the same, which is not surprising since both processors use the same clock rate for their lowest p-state. Even when we tweaked the voltages, the system power consumption would only drop to 66 watts.
Note: the Athlon II X4 620 and Phenom II X4 955 BE were neck in neck on the Socket AM3 platform, going down to 46 to 47 watts at idle. With practically no difference in idle power consumption between the two, the variables to consider are price and performance. When you factor in the ability to use an unlocked multiplier, the Phenom II X4 955 BE brings more to the table.
We also measure consumption without undervolting. The result was that the Socket AM3 platform consumes about the same power as the AM2/AM2+ when undervolted. So, if you want low power consumption without changing BIOS settings or hacking p-state values, the AM3 platform is the clear and logical choice.