[iMore.com]

Time Machine is OS X's built-in backup software. It was introduced with OS X 10.5 "Leopard" and has been there ever since. If you've never used it, please start. Time Machine is absolutely the easiest way to back up your Mac, and is great for recovering individual files you've deleted or restoring your entire hard drive in the event of a catastrophe.
In this how to, I'm going to cover two aspects of using Time Machine - how to set it up initially and how to restore individual files. You can also use Time Machine to restore the entire contents of your hard drive with your OS X Recovery Partition.

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