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  Transmeta's Crusoe, HotRod or Performance Hog? 
  May 11, 2001, 06:00am EDT 

Power Management

By: Sander Sassen

Most conventional x86 processors regulate power consumption by rapidly alternating between running the processor at full speed and turning it off. Different performance levels can be obtained by varying the on/off ratio, or 'duty cycle'. This approach has quite a few drawbacks, as, for example; the processor may just have been switched off when an application needs it, or it may be running at full speed when not being used at all at all.

The Transmeta Crusoe adjusts power consumption on the fly by dynamically increasing or decreasing clockspeed. As a result, software continuously monitors processor demand and dynamically selects the appropriate clockspeed needed to run the application, no more and no less, hence also managing the processor's power consumption.

Finally, the Code Morphing software adjusts the processor's core voltage on the fly. Because power varies linearly with clock speed and by the square of the voltage, adjusting both can produce huge reductions in power consumption, while a conventional processor can adjust power only linearly. For example, assume an application program only requires 90% of the processor's speed. On a conventional processor, throttling back the processor speed by 10% cuts power by 10% Under the same conditions, Crusoe's 'LongRun' power management can reduce power by almost 30% (30% = 100% x (1-(.9 x .92))).

1. Introduction
2. Code Morphing
3. Execution, Decoding, Scheduling
4. Caching and Optimization
5. Power Management
6. Conclusion

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