i've purchased a notebook last week(HP nx9005),
XP Home edition was pre installed.
The cpu speed was changing according the usage,for example when doing nothing, it was ~600 mhz, when rendering it was ~1.8 Ghz. Everything was fine.
But i reinstalled WindowsXP again yesterday,and now the cpu speed is always 1.8 ghz like a desktop cpu. How to make it changable again?

Go to the control panel -> power options and put it's power scheme to laptop (or was it "portable computer"). If that still doesn't work, you can download an utility on AMD's website that will enable you to control PowerNow! -features.

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In the fullness of time. Expect me when you see me.