Intel L5408 EU80574JH046N Data Sheet

102

Enhanced Intel SpeedStep Technology creates processor performance states (P-states) 
or voltage/frequency operating points which are lower power capability states within 
the Normal state (see 

 for the Stop Clock State Machine for supported P-

states). Enhanced Intel SpeedStep Technology enables real-time dynamic switching 
between frequency and voltage points. It alters the performance of the processor by 
changing the bus to core frequency ratio and voltage. This allows the processor to run 
at different core frequencies and voltages to best serve the performance and power 
requirements of the processor and system. The Quad-Core Intel® Xeon® Processor 
5400 Series has hardware logic that coordinates the requested voltage (VID) between 
the processor cores. The highest voltage that is requested for either of the processor 
cores is selected for that processor package. Note that the front side bus is not altered; 
only the internal core frequency is changed. In order to run at reduced power 
consumption, the voltage is altered in step with the bus ratio.

The following are key features of Enhanced Intel SpeedStep Technology:

• Multiple voltage/frequency operating points provide optimal performance at 

reduced power consumption.

• Voltage/frequency selection is software controlled by writing to processor MSR’s 

(Model Specific Registers), thus eliminating chipset dependency.

— If the target frequency is higher than the current frequency, V

CC

 is incremented 

in steps (+12.5 mV) by placing a new value on the VID signals and the 

processor shifts to the new frequency. Note that the top frequency for the 

processor can not be exceeded.

— If the target frequency is lower than the current frequency, the processor shifts 

to the new frequency and V

CC

 is then decremented in steps (-12.5 mV) by 

changing the target VID through the VID signals.