Time Machine

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Screen shot of Time Machine with OS X Lion
Screen shot of Time Machine with OS X Lion



Time Machine is a feature of first introduced within Mac OS X 10.5, and included within all subsequent Mac OS X releases. Time Machine allows for incremental backups of files that can be restored at a later date. Integrated into Finder, Time machine shows a timeline which allows the user to move through the history of all backups on the disk. The user can also use Spotlight to perform searches for specific documents and iPhoto to find deleted photos.

Time Machine can back up to a non-booting hard drive or server (inc Time Capsule).

The importance of backup was emphasized when Time Machine was announced at WWDC 2006, when Steve Jobs revealed that only 26% of users performed a backup of some kind, while just 4% performed an automatic backup.

How it works

Time Machine creates a folder on the designated Time Machine volume which is named the current date and time. It then copies all locally attached drives (except for excluded files/folders) to the folder.

Every hour thereafter, it creates a new folder on the designated volume using the same naming scheme, but instead of making another complete copy of the primary hard drive, Time Machine instead only backs up files that have changed and creates hard links to files that already exist on the remote drive. A user can browse these "versions" of the primary drive and see each file as if it were right where it was left.

One of the features in the Migration Assistant interface is to re-install the contents of a Time Machine backup. In other words, a hard drive can be restored from a Time Machine backup in the event of a hard drive failure.


Time Machine places strict requirements on the backup storage medium. The only officially supported configurations are:

  • A non-booting hard drive or partition connected directly to the computer, either through USB or Firewire, and formatted as journaled HFS+.
  • A folder on a journaled HFS+ file system shared by another Mac on the same network running at least Leopard.
  • A drive shared by an Apple Time Capsule on the same network.