If you are worried about installing the latest version of the MacOS on your Mac, or if you are testing out a beta version and don't want to run any risks, you don't have to install the update on your Mac at all - you can install it on an external hard drive.

Installing the Mac operating system on an external drive is the safest way to get a good look at a new operating system without changing anything on your Mac. It'll leave your current configuration intact and allow you to play around with Sierra or the successor to Sierra when the beta becomes available. Read about the next version of MacOS here, and how to get on the macOS public beta here.

In this tutorial we will show you how to run MacOS from a external drive.

What you'll need:

You'll want to use a fast drive if you can - Thunderbolt drives are comparable to the internal drives on a Mac so it's worth investing in a Thunderbolt drive. If Thunderbolt isn't practical, at least make sure that you opt for flash storage.

That drive will need to offer at least 12GB of space - but more is recommended.

What you need to do:

Follow these instructions to prepare your external drive:

  1. Connect the external hard drive.
  2. Launch Disk Utility (press cmd+spacebar and start to seatch for Disk Utility).
  3. Select the drive in the sidebar (the root drive, not the volume it contains).
  4. Click Partition.
  5. Ensure that Partition Layout says 1 Partition.
  6. Give it a name like "macOS Sierra".
  7. Click Options and ensure that Guide Partition Table is selected. Click OK.
  8. Click Apply and Partition.

Now download the macOS Sierra installation from the Mac App Store (or which ever version of the Mac OS you require - you can find older versions under the Purchased tab) and follow these instructions to install the beta on the external drive:

  1. Download the macOS Sierra installer from the App Store, and open it once downloaded.
  2. Click Continue.
  3. Click Agree and Agree.
  4. Click Show All Disks.
  5. Highlight the external hard drive.
  6. Click Install.
  7. Enter your Admin password
  8. To run Sierra, open System Preferences > Startup Disk. Select the drive you wish to start up the Mac and click Restart.
  9. You can also hold down Option/Alt during startup to pick the drive you wish to use to start up the Mac.

For more advice about installing MacOS or Mac OS X read: How to update the Mac operating system as well as How to download and install old versions of OS X on a Mac and How to make a bootable macOS install drive plus How to clean install macOS