One of the new features in OS X Mountain Lion is called Power Nap. Touted as a tool that get things done while your Mac is sleeping, Power Nap enables a Mac running Mountain Lion to download email, sync with iCloud, check for system updates, etc. while in sleep mode. There is a big caveat, however. Power Nap will only run on Macs with an internal solid-state hard drive (SSD).
During the developer beta phase of Mountain Lion and continuing into its public release stage, it was noticed that certain compatible Macs didn’t have Power Nap installed by default on the final release of Mountain Lion. Apple has since issued a firmware update to bring Power Nap to the MacBook Air, and now a new update today has been issued for the new MacBook Pro with Retina display.
MacBook Pro Retina SMC Update v1.0 is available now in the Mac App Store as a free update for Mountain Lion. According to Apple:
This update fixes several sleep/wake issues to improve the stability of MacBook Pro with Retina display (Mid 2012) computers and is recommended for all users running OS X v10.7.4.
It also enables Power Nap support for users running OS X v10.8 or later.
Once installed, Power Nap should be available under the Energy Saver settings in System Preferences. As Apple notes, even users on OS X Lion are asked to install the update as well, although Power Nap will only be added on Mountain Lion.