Power Policy Settings
Power plans and schemes consist of preferences and policy settings.
A power plan consists of a group of power setting preferences. These preferences consist of both an AC and DC value for each of the power settings. Each power plan is identified through a unique GUID as well as a friendly name. Windows Vista has three default power plans: Power Saver, Balanced, and High Performance. These plans can be customized, and additional plans can be created. All power plans have a personality attribute that indicates the overall power savings behavior of the plan.
The following table shows the three power plan personalities.
|Power Saver||Delivers maximum power savings at the expense of reduced performance.||a1841308-3541-4fab-bc81-f71556f20b4a|
|Balanced||Automatically balances performance and power consumption according to demand.||381b4222-f694-41f0-9685-ff5bb260df2e|
|High Performance||Delivers maximum performance at the expense of higher power consumption.||8c5e7fda-e8bf-4a96-9a85-a6e23a8c635c|
Each computer has a single, active power plan. By default, nonprivileged users are able to access system power settings. Access to all or individual power settings can be controlled through ACLs on the power settings or through Group Policy. Applications should call PowerSettingAccessCheck to determine if the user has access to the power setting.
Each power setting is identified by a unique GUID and includes a friendly name, description, allowable values, and default values for AC and DC. Custom power settings can be created using the PowerCreateSetting function.
A power scheme consists of several types of power policy settings:
- Global user. These settings apply to all power schemes for a user. For more information, see GLOBAL_USER_POWER_POLICY.
- Global computer. These settings apply to all power schemes for all users on the computer. For more information, see GLOBAL_MACHINE_POWER_POLICY.
- User. These settings are unique to each power scheme for a user. A nonprivileged user can change these settings. For more information, see USER_POWER_POLICY.
- Computer. These settings are unique to each power scheme on the computer. Only users with administrator rights can change these settings. For more information, see MACHINE_POWER_POLICY.
- Processor. These settings apply to all power schemes on the computer if the processor supports performance control and C-states. For more information, see MACHINE_PROCESSOR_POWER_POLICY.
Not all user policy settings are exposed to the user in the Power Options application in Control Panel. Some examples of user policy settings that are accessible include the minimum system idle time before the display is turned off, and the system power action to initiate (sleep state to enter) when the system is running on AC (utility) power and the system idle timer expires.
A number of power policy structures begin with a Version member. This need not be set before passing a structure to a function to retrieve data. However, the data retrieval functions do fill in this member with a valid value, which is required to set policy using the set or write functions. Therefore, to change policy settings, first retrieve current settings into an appropriate structure, make the desired changes, and then use the same structure to set the new policy.
Build date: 10/26/2012