updated 01:00 am EDT, Thu July 26, 2012
Firmware patch restores feature in Mountain Lion
Although a new feature called Power Nap was supposed to be part of the Mountain Lion install available today, some owners of recent MacBook Air and Retina MacBook Pro models have reported the feature missing from the Energy Saver system preference. For some, reinstalling the new Mountain Lion has fixed the issue, but late yesterday Apple issued a firmware update for mid-2011 and newer MacBook Airs to restore the Power Nap feature.
Power Nap is designed to allow a SSD-equipped notebook Mac to carry on some sync and other routine tasks even while sleeping, particularly backing up to Time Machine and doing iCloud synchronizations, a real time-saving feature for most Mac owners. The feature will also download (but not apply) software updates automatically if the machine is connected to a power source at the time. Apple has crafted the feature to handle these tasks without waking up the Mac or running the fans.
Currently only the SMC Firmware Update for the MacBook Air models is available -- the Retina MacBook Pro update is still listed as "coming soon." Once applied and the machine restarted, the Power Nap feature should then be available in the Energy settings of System Preferences.
The tech note detailing the firmware update also mentions additional abilities of the Power Nap feature, including VPN on demand (email can be downloaded while sleeping, even from secure servers if certificates are used for validation), Find My Mac (a lost or stolen Mac can be found even while it is sleeping), and corporate configuration profiles can be updated. In addition, Power Nap allows updates to Help Center, Spotlight indexing and Mac App Store update downloads if the machine is connected to power.
By default, Power Nap is turned off when a machine is running on battery power, but users can override this option. If the battery hits 30 percent capacity remaining, Power Nap will suspend itself. According to Apple, Power Nap checks every hour for routine iCloud, email and other sync operations such as a Time Machine backup. Software Update is checked only once per day and the Mac App Store is checked only once per week.