How to Connect an External Drive to Your iMac

By Mark L. Chambers

With Thunderbolt, USB or FireWire, you can install an external hard drive without opening your iMac’s case. With your iMac turned on and the external drive disconnected from the AC outlet, follow these steps:

  1. Connect the FireWire, Thunderbolt, or USB cable betwixt the drive and your computer.
  2. Plug the external drive into a convenient surge protector or UPS (uninterruptible power supply).
  3. Switch on the external drive.
  4. If the drive is unformatted (or formatted for use under Windows), partition and format the external drive. The drive comes with instructions or software to help you do this. (Don’t worry, external drives typically come from the factory completely empty, and you won’t damage anything by formatting it. To be sure, check the drive’s manual.) Partitioning divides the new drive into one (or more) volumes, each of which is displayed as a separate hard drive under El Capitan.

If the drive comes preformatted for use with a Windows PC, you really should consider reformatting it for use with OS X. Doing so results in faster performance and more efficient use of space.

After the drive is formatted and partitioned, it immediately appears on the Desktop. Shazam!