i forgot what its called but the processor changes multiplers to save power when comp is idle. i.e. it uses 16x * 200mhz in use and 12x * 200mhz in idle.
Enhanced Intel Speedstep Technology
newegg: Enhanced Intel SpeedStep Technology (EIST)
EIST allows the system to dynamically adjust processor voltage and core frequency to decrease average power consumption and average heat production. Combined with existing power saving features, EIST may provide an excellent balance between providing power when you need it and conserving power when you don't.