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Using Time Machine in macOS

Users of macOS have the option of using Time Machine with an external hard drive. Time Machine is an easy-to-use and completely automated incremental backup for your computer. This page covers getting a drive setup to work with it. For usage instructions use the Help menu on your computer and search for Time Machine.


  • Time Machine is only intended as a data recovery service for the computer it is installed on. You should not delete files on your computer and assume they are safe on Time Machine.
  • If you get a new computer that is a different model, Time Machine may restore the entire operating system to it, but due to differences in hardware, your new computer may not boot or have problems with some of its features. CTS does not support restoring a Time Machine backup to a new computer.
  • A Time Machine backup used on an old computer cannot be used on a new computer. In other words, if you get a new campus computer you must start erase your current Time Machine drive and start over.
  • A re-imaged campus computer will sometimes not see a previous Time Machine backup. We are a corporate-level network with Active Directory, and as such, a re-imaged computer may receive a different identity when it is added back into our systems. This will cause Time Machine to possibly see your computer as a different one, which causes it to restart a backup and ignore previous backups. This is normal and somewhat expected, Time Machine is a consumer level service and not designed with corporate networks and systems in mind.

Using A New Hard Drive

As soon as OS X detects an external hard drive attached, it immediately asks if you would like to use it with Time Machine.


Clicking Use as Backup Disk will automatically enable Time Machine and begin the initial backup of your computer. You can also tell it was successful because your hard drive icon has inherited the Time Machine icon.


Using An Existing Hard Drive

If you've previously declined to use your external hard drive for Time Machine and now have changed your mind, you can enable it via the Time Machine System Preference.

  1. From the Apple Menu, open System Preferences... locate the Time Machine icon and click it.
  2. Click Choose Backup Disk...
  3. Select your disk and then click Use for Backup. Clicking Use for Backup will automatically enable Time Machine and begin the initial backup of your computer.