Cool & Quiet In Detail

06:00 - Monday 1 December 2003 by Patrick Schmid
Source: Tom's Hardware – Keywords: generation, change

Cool & Quiet In Detail

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Cool & Quiet is not complicated at base. AMD has defined what it terms P States (processor performance states), each of which represents a combination of processor voltage and frequency. AMD's PowerNow! software has to be installed on systems running older versions of Windows. The software receives a Performance State Block (PSB) from the motherboard BIOS. The PSB is nothing more than information about the supported P States of the processor in use.

Current operating systems actually support the P States and only require a small extra driver that handles the transition from one P State to the next. To do that, it takes an ACPI compliant P State object from the BIOS containing all the necessary information on supported and possible P States.

A P State transition always occurs in three steps: first, the voltage is adjusted to accommodate the change in clock speed. Then the speed is adjusted. Finally, the voltage is adjusted to the speed defined in the respective P State.

The Athlon64 supports frequency changes of 200 MHz at a time; details on the correct way to do this are available at BIOS and Kernel Developer's Guide on AMD's website.


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