OnNow Power Management

[This is preliminary documentation and subject to change.]

Computers that comply with OnNow are designed to be instantly accessible to users at the touch of a button. As with appliances, the computer must always be on and ready for use, but appear to be off when not in use. This state of low power consumption is called the sleeping state.

When the computer is in the sleeping state, the computer hardware, the system, and applications running on the computer must be capable of responding immediately to the power switch, communications events, and other actions. If all applications handle power state transitions gracefully, the user will perceive a more elegant and integrated system. Applications that do not handle these transitions can fail when the power is turned off and then on, because of data loss or a dependency on a device that may have been removed.

The following are other benefits of OnNow:

• Eliminates startup and shutdown delays. The computer need not perform a full system boot when starting or a full system shutdown when turned off. Instead, the computer enters and leaves the sleeping state.
• Enables automated tasks to run while the computer is "off." The Task Scheduler provides a user interface that enables the user to schedule applications to run, even when the system is in the sleeping state. The Task Scheduler uses waitable timers to ensure that the system is ready when the application is scheduled to run. For more information, see the help file included with the Task Scheduler.
• Enables per-device power management. Devices that are not in use can save power by entering the sleeping state.
• Improves power efficiency. Power efficiency is particularly important on portable computers. The life of a battery on a portable computer is significantly reduced by use of the CPU and hard drive. When the computer is running on batteries, the system attempts to put the CPU and hard drive into a low power state whenever they are idle.
• The Power Management control panel application provides a simple user interface through which the user can specify preferences. The user can create power schemes, set alarms, and specify battery options. The operating system coordinates all power management activities, based on power management policies. For more information, see the help file included with the Power Management control panel application.