Updating to the latest version of macOS doesn't have to be an all-or-nothing affair. It's possible to install two different operating systems on your Mac and dual-boot them, which means they're both on there at once and you can choose the one that suits you on a day-by-day basis.
In this article we explain how to set up a dual boot on your Mac, but first you might like to know the benefits that this offers. (For OS options beyond macOS, you might like to read our guides showing How to install Windows on a Mac, and How to install Linux on a Mac.)
Why dual-booting macOS is a good idea
There are a few reasons why you might want to run two versions of the Mac operating system:
- If you want to update your Mac to the latest software but you have legacy apps that may not run on it.
- If you're a software developer and need to test your own apps on different versions of macOS (particularly if you need to do this regularly).
- If you want to safely try out a beta version of the Mac operating system without committing to it.
How to dual-boot two versions of macOS
In brief, here's how to set up your Mac so you can run two versions of the macOS operating system on it:
- Back up your Mac.
- Partition your hard drive.
- Install the older version of macOS (or Mac OS X) in partition 1.
- Restore your Time Machine backup to that partition.
- Install the newer version of macOS in partition 2.
Read on for more detail of each step.
Back up your Mac
This is the first step because when you partition your Mac you will have to completely wipe it.
If wiping your Mac sounds like too much hassle to you, you could try installing MacOS on a external hard drive instead. We show you how here: How to run macOS from an external hard drive.
If you want to keep your current work, you need to create a backup of your Mac and ensure it will fit on your smaller partitioned drive.
Partition your hard drive
You can partition the main hard drive into two separate drives and then install macOS High Sierra on one and Mac OS X 10.11 El Capitan on the other, for example.
In a separate article we explain how to partition your Mac hard drive or SSD.
Alternatively, create your partition by following these instructions:
- Boot macOS into recovery mode (hold down Option/Alt during startup).
- Use Disk Utility in recovery mode to wipe the main hard drive and split it into two partitions.
Install the old version of macOS in partition 1
- Use the Install option in Recovery to install OS X 10.11 El Capitan (or whichever version you've chosen) on to the main partition.
- Recover your Time Machine backup into that partition.
Install the new version of macOS in partition 2
Follow the steps above to install macOS High Sierra, or the beta of the new version of macOS, on to the second partition.