Apple has released a firmware update for 2011 and 2012 series MacBook Airs, enabling the Power Nap feature in the latest version of OS X. Released yesterday, Mountain Lion uses the feature to perform actions such as updating and processing notifications while the computer is ostensibly powered down, creating a smoother transition between sleeping and waking modes.
The system management controller (SMC) update is currently available for download via Apple's support site, with specific versions for the mid-2012 and mid-2011 Airs. Power Nap will not be supported on the late-2010 model or any earlier versions, but a firmware update is apparently "coming soon" for the new MacBook Pro with Retina display.
Users planning to upgrade should be aware that the package causes the machine to spin its fans at full speed for the duration of the flashing process — don't be alarmed if your beloved MacBook sounds like it's about to take off.