macOS High Sierra is a working beta, but what if you want to keep a copy of macOS Sierra, too?
If you are preparing to test out macOS High Sierra, there is one additional set of steps you should follow. You should download a bootable copy of macOS Sierra. This allows you to use it if you partition your hard drive for dual-software installation. It is also the only way to downgrade to the older format if you decide you don’t like macOS High Sierra at all.
Before you start
Before you get started, make sure you have a thumb drive with at least 8GB of storage, or a spare external hard drive (one that you don’t use with anything else).
You’ll also need to download macOS Sierra from the Mac App Store.
Note: After macOS Sierra has downloaded, it will automatically begin the installation process. Close the installer instead.
Please, Please, Please, backup your Mac before you do anything.
How to format your external drive for Mac
You’ll need to start with a clean thumb drive or hard drive in order to get it ready to work as a bootable drive.
- Plug the USB end of the drive to a USB port on your Mac.
- Click on Finder in your Dock to open a Finder window.
Select Applications from the list on the left side of the window.
- Scroll down and double-click on Utilities.
Scroll down and double-click on Disk Utility.
- Select your drive under External.
Click on the Erase tab at the top of the window.
- Note the name of your external hard drive (probably “Untitled”) because you will need it when you create a bootable drive. If you have more than one external hard drive named “Untitled,” you will need to rename your hard drive now.
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