A. Pre-Vista Windows versions had options to hibernate, which saved the computer's memory state to disk followed by a shutdown, and standby, which placed the computer into a low power-consumption mode. Vista has the sleep and hybrid sleep modes. In the basic sleep mode, the computer enters a low power-consumption mode, keeping programs and data state in memory; in hybrid sleep mode, the computer enters a low power-consumption mode, keeping programs and data state in memory but also writes the memory content to disk, which means in the event of a power outage the computer's state can be recovered from the disk version of the memory state. Hybrid sleep takes slightly longer to go into low power-mode because the memory content has to be written to disk. On my computer, sleep takes 2 seconds to enter, whereas hybrid sleep takes 16 seconds. The extra 14 seconds is worth it to avoid losing data in the event of a power outage.

The Sleep button on the computer puts the computer into sleep or hybrid sleep mode, depending on the configuration of the computer:

  1. Start the Power Options Control Panel applet (Start, Control Panel, Power Settings).
  2. Select the "Change plan settings" option for the current power plan.
  3. On the settings dialog box, click the "Change advanced power settings."
  4. Scroll down to the Sleep option, expand "Allow hybrid sleep" (on a laptop additional options for On battery or Plugged in" will be displayed) and click On or Off to allow/disallow hybrid sleep, as the figure shows.
  5. Click OK and close open dialog boxes.
This setting updates the ACSettingIndex (1 for enabled, 0 for disabled) under the HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Power\User\PowerSchemes\<GUID of scheme> key.