Understanding Power Management

The goal of power management in Microsoft Windows is to maximize energy efficiency. This is accomplished by minimizing the amount of power used while automatically providing required performance on demand. Previous versions of Windows delivered improvements in the area of power management, such as hibernation, standby, and the ability to power off monitors and hard drives. Windows Vista builds on these advances with new power-management capabilities, including:

• Improved support for Advanced Configuration and Power Interface (ACPI) 2.0. In addition, Windows Vista also provides support for selected features of ACPI 3.0.

• Standard (non-ACPI) Hardware Abstraction Layers (HALs) are no longer supported in Windows Vista; only the ACPI Programmable Interrupt Controller (PIC) HAL and ACPI Advanced Programmable Interrupt Controller (APIC) HAL are supported now in Windows Vista.

• Simplified power plan model, including three default power plans:

  • Balanced Automatically balances system performance with energy consumption—for example, by speeding up the processor when performing CPU-intensive activities, such as playing a 3D game, and slowing the processor down when performing activities that require little CPU, such as editing a document in Microsoft Office Word. Balanced is the default power plan in Windows Vista.

  • Power Saver Saves power at the expense of maximum performance. On mobile systems, this helps to maximize battery life. On desktop and server platforms, it works to reduce energy consumption.

  • High Performance Maximizes system performance at the expense of power savings.

• Mobile users can easily switch between power plans using the enhanced battery meter in the notification area or the battery tile in Windows Mobility Center. Desktop and server users can switch power plans in Power Options in Control Panel.

• OEMs can customize the default power plans or create their own and install them as the system default. In addition, users can easily create their own custom power plans and manage them.

• A new Sleep mode called Hybrid Sleep is available. It combines the benefits of Standby and Hibernation. When the system transitions to Hybrid Sleep, a hibernation file is generated, and the system transitions to Sleep (ACPI S3 state). Sleep and resume time are improved, because in most cases, the system is resuming from memory (ACPI S3). In the event of a power failure, system state is still preserved and the computer will resume from the hibernation file.

• Sleep reliability improvements. Windows Vista does not query applications or services before transitioning to any of the sleep states. This is a departure from how Windows XP behaves. Applications may no longer prevent the system from going to sleep when a user clicks the Sleep button or closes the lid on a mobile PC. This helps prevent the system from accidentally remaining powered on when in a laptop bag or other closed environment.

• Resume performance improvements. Waking from Sleep mode is much faster, and improved power transition diagnostics help ensure consistent and predictable power transitions.

• Support for managing power settings using Group Policy. This allows businesses to easily configure the policies for powering off monitors and computers after a period of inactivity, saving money in utility expenses.

• Extensible power settings. Third-party drivers and applications can add new power settings to the system, and custom power settings can be managed in the same manner as system power settings.

• Standard (non-Admin) users can now modify most power settings on their computers. Administrators can use standard security descriptors to control access to settings on an individual power setting basis.