One of the new features in OS X Mountain Lion is the PowerNap energy-saving option that allows newer MacBook Pro and MacBook Air systems to continue to use network and backup services when in sleep mode. However, even after installing the OS X Mountain Lion upgrade, qualified systems may not be able to use the PowerNap feature.
When activated in the system's Energy Saver system preferences, PowerNap will perform hourly checks for new e-mail and updates to Contacts, Calendars, Reminders, Notes, iCloud documents, and Photo Stream. It will also maintain a connection for Apple's Find My Mac service. Backups and software updates can also be kept active, with hourly backup attempts until a full backup is completed, and software update services running daily for system updates and weekly for App Store updates.
PowerNap is also power-source dependent, meaning it will only perform some of these features when plugged into an AC power outlet. The AC-dependent options include maintaining Time Machine backups and Spotlight indexing, as well as updating the system using the Mac App Store.
These details not only keep the system up to date, but in doing so prevent the computer from initiating a flood of updating activity whenever it is woken from sleep, which sometimes can cause significant lags in activity while programs hang and wait for their updates.
PowerNap is unfortunately not available for all Mac systems, and only works for any portable that contains built-in Flash storage. These include the 2011 through 2012 MacBook Air and the latest 2012 MacBook Pro with Retina Display. Non-retina MacBooks and older MacBook Pro models are not included, even though they can be configured with optional SSDs.
Despite being supported for using PowerNap, after installing Mountain Lion it may not be available on these systems. This is because PowerNap requires an SMC firmware update in order to work, which for now is only available for the supported MacBook Air models. If you are using a MacBook Pro with Retina Display, then you will have to wait for Apple to issue the firmware update for this model in order to use the PowerNap feature. These updates should be installed along with Mountain Lion, but can also be downloaded and applied from the following Web sites:
The update for the MacBook with Retina Display should be out soon, and when Apple releases it you will be able to install it using Apple's Software Update service.