PowerNow!

AMD PowerNow! is AMD's dynamic frequency scaling and power saving technology for laptop processors. The CPU's clock speed and VCore are automatically decreased when the computer is under low load or idle, to save battery power, reduce heat and noise. The lifetime of the CPU is also extended because of reduced electromigration, which varies exponentially with temperature.
The technology is a concept similar to Intel's SpeedStep technology. The adaptation of PowerNow! for AMD's desktop CPUs is called Cool'n'Quiet. Newer Opterons also use an adaptation of PowerNow! called "Optimized Power Management."
AMD has supplied and supported drivers for its PowerNow! technology that work on Windows 98, ME, NT, and 2000. 
See also.
Power Saving Technologies:
Performance Boosting Technologies: