Power Nap

Available on Mac computers with flash memory (not for Mac computers with a hard disk or solid-state drive), Power Nap lets some Mac computers stay up to date even while they’re in sleep. When the Mac goes to sleep, Power Nap activates periodically to update information. The information that’s updated depends on whether your Mac is running on battery power or plugged into a power adapter.

When your Mac is in sleep and using battery power, Power Nap does the following:

• Checks for new messages in Mail

• Updates events in Calendar

• Updates other iCloud events

When your Mac is plugged into a power adapter, Power Nap can also do Time Machine backups.