Managing Power States

In Windows 7, the Advanced Configuration Power Interface (ACPI) specifies the following different levels of power states:

• Fully active PC
• Sleep
• Hibernation
• Complete shutdown of PC

The sleep power state is a new power state introduced with Windows 7 that combines the features of hibernate and standby. When a computer enters the sleep power state, data including window locations and running applications is saved to the hard disk, and that session is available within seconds when the computer wakes. This allows the computer to be put into a power-saving state when not in use but provides quick access to the in-process user session, thus enabling the user to begin working more quickly than if the computer were shut down or put into hibernation.

Hibernation falls short of a complete shutdown of the computer. With hibernation, the computer saves all of your Desktop state as well as any open files. To use the computer again, press the power button. The computer should start more quickly than from a complete shutdown because it does not have to go through the complete startup process. You will have to again log on to the computer. Similar to when the computer is put into Sleep mode, all the documents that were open when the computer went into hibernation are still available. With hibernation you can easily resume work where you left off. You can configure your computer to hibernate through Power Options or by choosing Start, and then clicking the arrow and selecting Hibernate from the drop-down menu. This option appears only if hibernation has been enabled through Power Options.

NOTE The Hibernation mode might not be available on your Windows 7 laptop by default. You must make sure that your firmware can support Hibernation.

If the Hibernation mode does not appear by default and your system can support Hibernation, perform the following steps to enable the Hibernate function:

1. Open an elevated command prompt. (Right-click the command prompt and choose Run As Administrator.
2. Click Yes at the dialog box.
3. At the prompt, type powercfg -h on and press Enter. Entering the same command and using the off switch would disable Hibernate on the machine.
4. Close the command prompt.

Now let's look at the various types of power options that you can configure.