Only 800 MHz and 0.992 V When Idle
As with its predecessor, the Phenom II comes equipped with AMD’s Cool’n’Quiet energy saving functions, so that when the processor finds itself idle, it can lower its clock rate and core voltages. In conjunction with the motherboard, the processor can even turn off unneeded voltage regulators. A first-generation Phenom can lower its clock rate to a minimum of 1,250 MHz because the smallest possible multiplier is set at 6.25.
In contrast, the Phenom 2 can drop its clock rate to a mere 800 MHz thanks to a minimum multiplier of 4.0. The 45 nm technology enables the core voltage to be dropped from 1.040 V to 0.992 V. AMD has been generous in the voltage range it permits for the Phenom II--the chip’s technical documents define operating ranges from as low as 0.875 V and as high as 1.5 V. This might mean that some processors do better or worse than others in terms of power savings. Another clock reduction at idle depends on the architecture and the production process. Stable operation of the processor at very low clock rates depends as much on capacitance and inductance in the system as it does on the switching rate of the transistors in use. This can sometimes entail a complete reworking of system structure before lower clock rates become usable.
The Phenom X4 9950 Black Edition lowers its clock rate to the same 1,250 MHz and lowers its voltage to 1.040 volts as well.
At idle, the Phenom II is more energy efficient, at 800 MHz and 0.992 volts.