One of OS X Mountain Lion’s lesser-known features is the curiously named Power Nap. It’s roughly analogous to that sleeping mountain lion you see at the top of this post; while he’s catching some z’s in the tree, his brain is constantly aware of what’s going on around him, monitoring sounds and scents that might spell danger or food.
Likewise, Mountain Lion Power Nap will wake up just enough of the system on certain Macs to grab email, notes, reminders and messages, run backups, and download OS X updates. All of this is done without turning on a screen, powering up a fan, or doing anything else that could appear to be “waking” your Mac. It’s enabled for both plugged-in and battery-only setups by checking the appropriate Power Nap box on System Preferences > Energy Saver.
Power Nap in OS X Mountain Lion works only on MacBooks with built-in flash storage — the MacBook Air (2nd generation, meaning 2011 or later) and Retina MacBook Pro, so this isn’t a feature you’re going to see on every Mac. Will we see this extending to more Macs in the future? I certainly hope so; it could theoretically work on any Mac with proper power management circuitry and a boot SSD.
I’ve enabled it on my 2011 MacBook Air and it works quite well. Previously, if I hadn’t awakened the MBA for several days, I could count on having the Mail app spin for quite a while as it downloaded my email. Now when I open my Air’s cover, I can be sure that it’s going to be up to date with most, if not all, of my email.
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