Power Management in Windows Vista

Eliot — Fri, 22 Feb 2008 01:29:00 GMT

Stephen, a program manager on the Windows Kernal team, posted a response to a question in the General Windows Vista Development Issues forum, and I thought it could bear repeating here. The original question was about how to control the processor throttle in Windows Vista. Apparently, some of the calls that used to work in an application geared to Windows XP were not acting the same way in Windows Vista. Here's Stephen's response:

Windows Vista and Windows Server 2008 use a new power policy infrastructure and API. This page details all the power APIs and indicates what is supported by the various Windows versions:

http://msdn2.microsoft.com/en-us/library/aa373163(VS.85).aspx

While some of the older APIs are supported in Vista, it is recommended that you use the new APIs on Windows Vista and later versions.

To give some background, in Windows Vista a power plan (sometimes called a power scheme) contains the power setting values that are actually in effect on the system. A power plan is uniquely identified by a GUID and contains an AC and DC values for each power setting. There can only be one power plan active at a time on the system. The current plan can be obtained using the PowerGetActiveScheme.

Like power plans, power settings are also identified by unique GUIDs and include a friendly name, description, allowable values, and default values for AC and DC. Power setting values can be modified using the PowerWriteACValueIndex and PowerWriteDCValueIndex routines. Note that you must call PowerSetActiveScheme after modifying any of the power settings in order to activate the new values.

Specifically to your question, there are two settings that allow you to adjust the minimum and maximum state for processor power management. These are expressed as a percentage of the maximum processor frequency. Here is a summary of these two settings:

Description	Minimum processor performance state. The performance state is specified as a percentage of maximum processor frequency.
GUID	893dee8e-2bef-41e0-89c6-b55d0929964c
PowerCfg Alias	PROCTHROTTLEMIN
Minimum Value	0
Maximum Value	100
Label	Percentage (%)
Hidden	No

Description	Maximum processor performance state. The performance state is specified as a percentage of maximum processor frequency.
GUID	bc5038f7-23e0-4960-96da-33abaf5935ec
PowerCfg Alias	PROCTHROTTLEMAX
Minimum Value	0
Maximum Value	100
Label	Percentage (%)
Hidden	No

Additional information on Vista power policy is described in detail in the following whitepaper:

http://www.microsoft.com/whdc/system/pnppwr/powermgmt/PMpolicy_Vista.mspx

Cheers,

Stephen [Microsoft]

RTM of the Windows SDK for Windows Server 2008 and .NET Framework 3.5

Eliot — Fri, 08 Feb 2008 00:19:00 GMT

Wow, this is a mouthful, but if you want the latest and greatest Windows bits this is hot out of the oven:

The Windows SDK team is proud to announce that the RTM release of the Microsoft Windows SDK for Windows Server 2008 and .NET Framework 3.5 is now live for customers to install! This SDK is a large product spanning both Windows and the .NET Framework.

Availability:

• The Windows SDK is available to install as either an:

• ISO, or

• Web Setup

Platforms:

This SDK release supports Windows Server 2008, .NET Framework 3.5, and Windows Vista SP1 and is compatible with Visual Studio 2008, and Visual Studio 2005 SP1; including Visual Studio Express Editions.

What’s New:

The following is a small sampling of what’s in this SDK, with a more complete list available in the Getting Started section in the Windows SDK documentation.

• Support for Windows Server 2008 (x86, x64, and Itanuim), .NET Framework 3.5, Windows Server 2003, Windows Vista (including SP1), and Windows XP

• Visual Studio 2008 C++ command line compiler toolset (with /analyze support) and matching CRT

• The SDK headers, libs, and tools integrate with VS2008 when both the SDK and VS2008 are installed

• New tools such as XPerf, SqlMetal, xsltc, gc, topoedit, aspnet_merge, and wsdcodegen.

• Documentation and samples (2200+ sample projects) to explain usage of new Windows Server 2008 and .NET Framework 3.5 features as well as previous platform features.

Learn More:

Stayed tuned to the Windows SDK blog as well as the Windows SDK MSDN Developer Center over the coming days and weeks for more information about the Windows SDK. As always, please look over the Release Notes for a description of known issues before you install the SDK.

As always, if you have comments or suggestions, use the MSDN Wiki or the built-in feedback mechanism in the SDK. Have questions, need help finding something? Post to the MSDN forums. There's a whole community there to help.

Happy coding!

Eliot's Blog : forums

Power Management in Windows Vista

RTM of the Windows SDK for Windows Server 2008 and .NET Framework 3.5