OS X Mountain Lion: Time Machine overview
When you connect your Mac to a new disk, a message appears asking if you’d like to use the disk to back up your files. Use this information to respond to the message.
- Use as Backup Disk: Time Machine will use this disk for backups. Initially, Time Machine makes a complete backup, including system files, applications, accounts, preferences, music, photos, documents—everything you keep on your computer, except for a few temporary files (such as web browser caches).
Depending on how many items you’re backing up, your initial backup could take a while. Subsequent backups take less time because only items that have changed are backed up. You can use your computer during backups.
Time Machine works best if you use your backup disk only for backups. If you keep files on your backup disk, Time Machine won’t back up those files, and the space available for Time Machine backups is reduced.
- Encrypt backup disk: For security, select this checkbox. If you back up to an external disk and do not encrypt the backup disk, any person who gains possession of the disk can read the information on it.
- Decide Later: Time Machine will display the message again each time you connect to the disk.
- Don’t Use: Time Machine will not ask again if you want to use this disk for backups.
If your Mac is in sleep or your backup disk isn’t available when it’s time for a scheduled backup, the backup is not performed. Backups resume after the computer and backup disk are available again.
If you have a portable computer, in addition to saving backups on your backup disk, Time Machine saves hourly snapshots of files and stores the snapshots on your computer’s internal drive. If your backup disk isn’t connected, Time Machine continues saving snapshots on your internal drive, and then resumes backing up to your backup disk when you reconnect it.