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Old 3rd July, 2004, 10:16 AM
Aedan Aedan is offline
Chief Systems Administrator
Join Date: September 2001
Location: Europe
Posts: 13,075

Originally Posted by Marcus Bertolli
Many of the earlier boards for AMD 64 (754 pin) only allowed for a 1.55 vcore.
The processor has a set of 'Voltage ID' pins (VID) that indicate the voltage that the processor is requesting. Unlike previous chips, the AMD64 CPUs have the ability to request different voltages in different operating states.

A 1.55v VCORE isn't over volting! In fact AMD's specifications state that the VCO requires an increase in voltage to 1.55v in order to remain stable through some ACPI state transitions. The processor itself changes the VID pins to enable this increase in voltage. During P state transitions, a stock processor will go through VCORE voltages of 1.45V, 1.475V, 1.5V, 1.525V and 1.55V. When the processor is idle, the processor's P state will leave the VID pins set to 1.45V.

The way that the bringing the VCORE voltage works is by adding an offset to reference voltage that the regulator uses. So, if you raise the voltage by 0.1V, then when the regulator thinks it's producing 1.5V, it's actually producing 1.6V. So, when you bring the voltage up in the BIOS, you're adding (or subtracting) a small voltage to the regulator's reference voltage.

It's documented under the power and thermal management section in the 'BIOS and Kernel Developers Guide for the AMD Athlon 64 and AMD Opteron processors'

Edit: fixed a typo
Any views, thoughts and opinions are entirely my own. They don't necessarily represent those of my employer (BlackBerry).

Last edited by Áedán; 3rd July, 2004 at 12:46 PM.
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