Use SpeedStep to Minimize Fan Noise even while laptop is plugged in – via Win XP command line

February 4, 2010 at 10:36 pm Leave a comment

If you want to save battery time or want to lower the fan noise in Win XP you can change the power settings. However non of the predefined power schemes uses low CPU speed while plugged in. Here is how you add such a profile:

— short version of the post —

Start a command-line as Administrator Privileges (for example via MachMichAdmin) and then do:

   REM List current energy profiles
   REM copy current profile with new name ‘LessFanProfile’
   REM change profile ‘LessFanProfile’ to use lower CPU speed all the time
POWERCFG /CHANGE LessFanProfile /processor-throttle-ac CONSTANT
POWERCFG /CHANGE LessFanProfile /processor-throttle-dc CONSTANT
   REM activate ‘LessFanProfile’

optionally you can do:

   REM List profiles, note the new addition


   REM Get a list of all properties of the profiles ‘LessFanProfile’

— long version of the post —

You can open the power setting dialog by calling


from the command line. (You might want to start this via command line, because you might want to work with a restricted user account. Then you can call MachMichAdmin [it’s a WinXP sudo offered by Germany’s publisher of the most professional computer information magazines. MachMichAdmin German Page in their Software Directory. The link to the MachMichAdmin info page (German). The direct link to the zip file of the MachMichAdmin batch files.] to get a shell with Admin privileges under your username. And from there you can call the dialog with Admin rights.)

However, it turns out that non of the profiles you find there enforces a lower CPU speed while the laptop is plugged in.

You can head over to Orthogonal Thought: Intel SpeedStep, Windows XP, and confusing Power Profiles and read what profiles does what. If you want a profile that throttles the CPU all the time, do the following:

Start the powercfg.cpl with Admin rights (in German: Energieoptionen)

Add another energy profile: you do this by clicking on “Save As”. This will copy the chosen Energy scheme, with the adjustments you made. I assume you choose the name “MyPowerConfig1LowCPUSpeed” for your profile after clicking “Save As” (but anything else will do). [You can see a picture of the Power Options Properties dialog in this blog post.]

Then go to a command line and try:


This will give you a list of your power schemes. “MyPowerConfig1LowCPUSpeed” should be one of them.

You can look at your new energy profile with


Then change the behaviour while on AC (plugged in) regarding SpeedStep by doing the following with Admin privileges (at least for Intel processors with SpeedStep)

POWERCFG.EXE /CHANGE MyPowerConfig1LowCPUSpeed /processor-throttle-ac CONSTANT

You can also change the behaviour while on battery by the following command:

POWERCFG.EXE /CHANGE MyPowerConfig1LowCPUSpeed /processor-throttle-dc CONSTANT

The keywords are CONSTANT = “CPU(s) run in lowest performance state”, ADAPTIVE = “adapts to CPU usage”, NONE = “CPU(s) run in highest performance state” (and there is a fourth keyword but it’s of no use) [Thanks again to Orthogonal Thought: Intel SpeedStep, Windows XP, and confusing Power Profiles for the information, go there to read it much better.]

You can now activate this profile from the Power Options dialog (run CONTROL POWERCFG.CPL) by choosing it from the drop down menu and pressing okay. I find this useful for the nights I want my computer to run but be very, very silent. When I activate this option, the fan won’t run at all, and I can sleep tight within the same room, even though the laptop (with the screen turned off) calculates some stuff (albeit slowly).


Entry filed under: hardware, software, WinXP. Tags: , , , , , , , , , , , , , , , .

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