Managing Power in Windows Vista

Windows Vista introduces four main power management improvements:

• A Power button on the Start menu that encourages the use of power-saving modes
• Restrictions on the ability of applications to interrupt sleep transitions
• A new user interface (UI) for managing applications that are blocking shutdown
• A simpler presentation of power management settings

The Power button on the Start menu encourages users to take advantage of power-saving modes on their computers, rather than relying on shutdown. Of course, users can always shut down. By default, the Power button puts a mobile PC to sleep (S3). This mode turns off most hardware on the mobile PC but maintains the RAM state. The user can quickly resume from standby with the same desktop configuration.

The following screen shot shows the Power button on the Start menu.

Note  Occasionally, Windows sets the Power button to shut down, such as when there are updates to install that require the computer to restart. On mobile PCs that lack BIOS support for either sleep (S3) or hibernate (S4), or on mobile PCs where either of these settings is disabled, Shut down, Restart, Hibernate, and Sleep appear, depending on which settings are available. A mobile PC that's configured with the Classic Start menu reverts to the behavior seen in earlier versions of Windows.

Desktop computers use a new power-saving mode called Fast S4. In this mode, the system goes into standby, but RAM contents are written to disk, just as they are in hibernate (S4 mode).

Application developers need to be aware of changes in the shutdown process in Windows Vista. The net result is that when users want to turn off their computers, they're much more likely to get what they ask for.

• Prior to Windows Vista, an application could veto a sleep transition by responding to the PBT_APMQUERYSUSPEND power broadcast. Now, applications cannot veto sleep transitions, although system administrators can allow applications to veto sleep transitions by using Group Policy.)
• Applications can still veto a shutdown by responding to the WM_QUERYENDSESSION message. However, Windows Vista provides a user interface for managing applications that are blocking shutdown.
• Applications can provide a descriptive string that explains why they're vetoing shutdown. For more information about creating the string for the shutdown procedure, see ShutdownBlockReasonCreate.
• Applications that don't have a top-level window or that stop responding are automatically closed when the computer is shutting down.

The following screen shot shows two applications that are blocking Windows from shutting down.

In Power Options in Control Panel, users can choose the power management behavior that they want. Settings are collected into power plans, each of which has one of the following designated personalities:

• Balanced
• Power saver
• High performance

Besides clarifying options for users, the personalities make it easier to determine the overall intent of each power plan. Many users will use the default Balanced plan. However, users can easily switch among plans and also change settings for a plan.

The following screen shot shows selected power management settings in Control Panel.

Power management settings can change during an application session. Your application can be notified when settings change. For more information about power management interfaces, see The Power-Aware Application.

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Build date: 2/8/2011