AMD64 Clock Utility v1.0
 

A64CLK (AMD64 Clock Utility) is a simple utility designed for realtime CPU frequency monitoring and realtime adjustment of the CPU multiplier (FID) and voltage level (VID) of the upported CPUs via processor's power management model specific registers (MSRs). An AMD64 (AMD K8) family CPU supporting processor performance states transitions (known as AMD PowerNow!™ or AMD Cool'n'Quiet™ technology) is required. The presence of this feature is automatically detected at the program startup.

http://cpu.rightmark.org/