Windows Vista includes several additions and improvements for power management on mobile PCs such as notebooks and tablet PCs, but also for desktop PCs. One of the most notable additions is the new supported ACPI power state Sleep , which is basically a fast and more reliable standby mode that can save both energy and time. The different power states will be covered in a separate section later in these TechNotes and will first have a look at power plans and their power options.
Windows Vista allows users to select default or custom power plans that suit the computer and its use. A power plan is basically a collection of power options and settings that users can change according to their needs, and enables users to easily and quickly select a different power plan when needed. For example, when the user needs to deliver a presentation and wants the entire computer including screen and peripherals to stay on, the user can simply choose a power plan with the proper settings rather than having to configure individual power options again and again.
By default Windows Vista includes the following three standard power plans:
- Balanced - This plan attempts to provide a balance between performance and power consumption and is suitable for most systems.
- Power saver - This plan attempts to reduce power consumption as much as possible, to save energy, by lowering the CPU speed and .. The power saver plan is suitable for devices that need little processing power, such as Internet and email clients, and for maximizing the battery life.
- High performance - This plan ensures power consumption is not reduced at the cost of performance and is suitable for systems running resource-intensive applications.
Users can quickly switch to another power plan by clicking on the battery power indicator in the notification area of the Taskbar as depicted in the image on the right. By default Windows Vista uses the Balanced plan trying to minimize the required amount of power while still providing a decent experience to the user. This also means the Shutdown button on the Start Menu will put the computer in the default Sleep mode. With the Balanced plan as well as the Power Saver plan, the display is automatically turned off after 20 minutes of inactivity and the computer is put to sleep after one hour. With the High Performance plan, the display is turned off after 20 minutes but the computer will always remain on.
Power plans can be selected and configured through Power Options in the System and Maintenance section of the Control Panel as shown in the following image.
When you click on Power Options, the following screen will open. Here you can select a power plan, change plan settings. The list on the left of the screen provides a convenient way to change common options for the current power plan settings, as well as add a custom power plan by clicking Create a power plan .
When you click the Change plan settings option below any of the listed power plans, the Edit Plans Setting screen will open allowing you to change when the computer should turn off the display and when to put the computer to sleep, as well as the brightness setting of the display. These three settings can be configured for when the computer is running on battery and separately for when the computer is plugged in, and can have a drastic effect on power consumption.
The Change advanced power settings option opens the Advanced power settings window where you can view and change all of the settings that combined make up a particular power plan. These settings, listed below, can also be configured by Group Policy to be enforced by an administrator - in a domain environment for example - or by using the Powercfg.exe command-line utility that also allows you to export/import power plans. For mobile devices you can specify many of the options separately for when the computer is plugged in and on battery. The default values can differ per plan and some options are not available on all systems. For optimal use of this list, as well as the rest of these TechNotes it's essential to actually configure them in Windows Vista.
Additional Settings\Require a Password on wake up - if this is set to yes (default), Windows Vista will require the user to enter the password for his or her user account when a computer wakes up from sleep mode.
Hard Disk\Turn Off Hard Disk After - specifies the number of minutes of inactivity before the hard disk is turned off. To ensure the hard disk is never turned off this option can be set to Never.
Wireless Adapter Settings\Power Saving Mode - This option can be set to Maximum Performance, Low Power Saving, Medium Power Saving, or Maximum Power Saving to specify the power saving mode for wireless network interfaces.
Sleep\Sleep After - Specifies the number of minutes of inactivity before the computer is put to sleep. This option can also be set to Never.
Sleep\Allow Hybrid Sleep - Specifies whether the new Windows Vista sleep mode should be used or the older Hybrid Sleep. You can set this value to On or Off. Hybrid Sleep puts the computer to sleep but also writes RAM contents to disk. If power is unexpectedly lost because of a hardware failure for example, the session would still be available on disk.
Sleep\Hibernate After - Specifies the number of minutes of inactivity before the computer goes into hibernation mode. This option can also be set to Never, which is the default value because Sleep is the standard 'Off' mode in Windows Vista.
Power Buttons And Lid\Lid Close Action - This option specifies whether the computer should go to Sleep, Hibernate, Shutdown or do nothing when the user closes the lid of a notebook/laptop. The default value is Sleep.
Power Buttons And Lid\Power Button Action - This option specifies whether the computer should go to Sleep, Hibernate, Shutdown or do nothing when the user presses the Power button on the computer. The default value is Shutdown.
Power Buttons And Lid\Sleep Button Action - This option specifies whether the computer should go to Sleep, Hibernate, or do nothing when the user presses the Sleep button on the computer (if it has one). The default value is Sleep.
Power Buttons And Lid\Start Menu Power Button - This option specifies whether the computer should go to Sleep, Hibernate, or do nothing when the user click the power button on the Start Menu.
PCI Express\Link State Power Management - This option can be set to Off, Moderate Power Savings, or Maximum Power Savings to specify the power saving mode for PCI Express devices.
Processor Power Management\Minimum Processor State - This option allows you to decrease the CPU performance resulting in less power consumption. The lower this value, a percentage, the lower the processor will try to perform. For maximum performance set this option to 100%.
Processor Power Management\Maximum Processor State - Similar to the previous option but sets an absolute maximum percentage of processor power. Again the lower the value the less energy is consumed and the less the CPU will perform.
Search and Indexing\Power Savings Mode - This option allows you to balance indexing activity with power consumption. The possible values for this option are confusingly named after the default power plans.
Display\Turn Off Display After - This option specifies the number of minutes of inactivity before Windows Vista turns off the display. Instead of specifying the number of minutes, you can set this option to Never to ensure the monitor stays on.
Display\Adaptive Display - This option can be set to On or Off to specify whether Windows Vista automatically delays the above option based on mouse and keyboard usage.
Display\Display Brightness - Specifies the brightness level of the display as a percentage.
Multimedia Settings\When Sharing Media - This option specifies whether the computer can go to sleep when other computers or devices are playing media from this computer. It can be set to Allow the computer to sleep , to Prevent idling to sleep , or to Allow the computer to enter Away mode . (Away mode is covered later in these TechNotes).
Battery/Critical Battery Action - This option specifies the action Windows Visa should take when the battery reaches the level specified in the following option. It can be set to Sleep, Hibernate, Shutdown, and when plugged in to Do Nothing.
Battery/Critical Battery Level - This option specifies the percentage of remaining battery power that is considered critical.
Battery/Low Battery Level - This option specifies the percentage of remaining battery power that is considered low.
Battery/Low Battery Action - This option specifies the action Windows Visa should take when the battery reaches the level specified in the above option. It can be set to Sleep, Hibernate, Shutdown, and Do Nothing.
Battery/Low Battery Notification - This option can be set to On or Off to specify whether Windows Vista should popup a notification when the batter reaches the 'low' level.
Several of the above settings can also be configured through the following screen, which opens when you click one of the links in the menu on the left in the main Power Options screen. Here you can specify which action Windows Vista should perform when you press the power button, press the sleep button and close the lid. Additionally you can specify here whether a password is required when the computer wakes up from sleep. These options correspond with the advanced power options in the Additional Settings and Power Buttons section.
Windows Vista supports the following four ACPI power states :
- Fully Active PC
- Complete Shutdown
The first state is the same as 'On' and the last one is the same as 'Off'. When a computer goes into Hibernation - a power state introduced in Windows 2000 - a snapshot of the memory containing the user's workspace including open files, applications and windows is saved to a file on disk. When the computer starts again, Windows won't have to start up from scratch but will load the user's session from disk into memory. When a computer is hibernating, it does not require any power.
The new Sleep power state is now the default 'off' mode and works like a pause or standby button. When a computer enters Sleep mode, the user's session is saved to RAM and requires a very low amount of power to sleep. The main advantage of Sleep is that it allows the user to resume working very quickly, usually within a couple of seconds, while still being able to save a lot of power. On mobile PCs when the battery runs too low it will exit Sleep mode and go into hibernation to ensure no data is lost when the battery is dead. When the advanced setting Hybrid Sleep is turned on the session is written to both memory and a file on disk.
While power usage is primarily important on mobile devices running on battery, the Sleep mode is also beneficial for plugged-in PCs. Many desktop PCs are turned on for many hours a day but are often idle for many short periods per day. To reduce the power usage to a minimum when the computer isn't used, while still being able to continue working without long delays, the computer can be put in Sleep mode. Modern PCs in sleep mode will actually consume less power, which can have a noticeable effect on the electricity bill from large enterprises to home users.
Another 'mode' that Windows Vista can enter is Away mode , which allows users to keep their system running in case they share resources or perform other tasks for which the user doesn't actually need to operate the computer. When the PC enters Away mode, the display is turned off, sound is disabled, and keyboard and mouse input are ignored. Away mode is not a real power state. Although the PC will appear to be turned off, it will actually still run and consume power as normal. The latter is why Away mode is not recommended unless it's really needed. Once Away mode is enabled, any action that would normally put the computer into Sleep mode will now put the computer in Away mode. Pressing the physical On/Off button on the PC will exit Away mode. Away mode can
be set by media sharing applications when needed.
Following are some general tips for keeping power usage to a minimum and extending battery life:
- Remove flash cards from the drive when you don't use them.
- Lower the brightness of the display.
- Disconnect USB and IEEE1394/FireWire devices.
- Make sure you have sufficient memory, more pagefile swapping means more power consuming hard disk activity.
- Use ReadyDrive with Hybrid hard disks - less read/write activity of the mechanical hard disk that use more power than the flash drive.