A lesser known feature of Windows Power Schemes are the CPU throttling options that are tied to each Power Scheme.
Windows XP/Server 2003
There are 4 CPU throttling options available to control in Windows XP or Server 2003.
| Processor behavior | CPU Throttling |
|---|---|
| This parameter causes the microprocessor to operate at the highest performance state at all times. | None |
| This parameter modifies the performance state that is dynamically based on the demand the computer puts on the microprocessor (CPU). | Adaptive |
| This parameter causes the microprocessor to operate at the lowest performance state at all times. | Constant |
| This parameter causes the microprocessor to operate at the lowest performance state and reduces performance by applying stop clock throttling (also known as Linear Performance Reduction) as the computer battery drains. You typically use this parameter when the computer is operating on battery power and it is seldom used with /processor-throttle-ac. | Degrade |
The Built-In Windows XP power schemes use different CPU throttling settings based on whether the computer is plugged in (AC) vs. whether the computer is on battery (DC).
The following table shows the different CPU throttling setting used for each respective Power Scheme.
| Built-In Power Scheme | AC (Plugged in) CPU Throttling Setting | DC (On Battery) CPU Throttling Setting |
|---|---|---|
| Home/Office Desk | None | Adaptive |
| Portable/Laptop | Adaptive | Adaptive |
| Presentation | Adaptive | Degrade |
| Always On | None | None |
| Minimal Power Management | Adaptive | Adaptive |
| Max Battery | Adaptive | Degrade |
To manually control the CPU Throttling mode that is tied to each scheme, the Windows POWERCFG.EXE utility can be used. This is the utility that does the behind-the-scenes work for the Power Options applet in the control panel. LANDesk Power Management manipulates the registry directly to control Power Settings for Windows 2000,XP, and 2003. For Windows Vista, Server 2008, and Windows 7 the Power Management function calls are used.
The command line options for CPU Throttling are as follows:
AC (Plugged In)
C:\Windows\System32\PowerCFG.exe /change "Power Scheme Name" /processor-throttle-ac <throttle setting>
DC (Running on battery)
C:\Windows\System32\PowerCFG.exe /change "Power Scheme Name" /processor-throttle-dc <throttle setting>
Example: C:\Windows\System32\PowerCFG\.exe /change "Home/Office Desk" /processor-throttle-dc none will change the CPU throttle setting for the power scheme named "Home/Office Desk" to None.
LANDesk Power Schemes
When deploying a LANDesk Power Scheme, the power settings are set to the default CPU Throttling settings of "Adaptive" for AC, and "Adaptive for "DC". This represents the best balance between power savings, and performance.
This setting is also configurable when using a LANDesk Power Scheme. You have the following options to choose from:
In order to view the specific settings in place, please use the following command:
"C:\Windows\System32\Powercfg /query"
To check the current operating frequency of the CPU, you can check the My Computer --> Properties screen.
The first frequency listed (in this case 3.00ghz) is the base frequency the CPU should run at (Max frequency).
The area marked in red is the actual frequency the CPU is currently running at. Typically when the CPU is throttled it will run at 50% of the maximum frequency.
This is only checked at the time the My Computer --> Properties screen is open. There are many third-party utilities that will show the operating frequency of the processor in real-time.
Note: For many computers it is necessary to install the vendor's power management drivers in order for the CPU throttling options to work correctly.
Check the drivers section of your computer vendors website for "Power Management Driver" or "Power Manager".
Further information regarding Windows Power Schemes is available in the following Microsoft Knowledgebase Article: