What's the difference between Windows Vista's sleep and hybrid sleep modes?

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:

This setting updates the ACSettingIndex (1 for enabled, 0 for disabled) under the HKEY_LOCAL_MACHINESYSTEMCurrentControlSetControlPowerUserPowerSchemes key.