Updating to the latest version of macOS, or running a beta version of macOS on your Mac, 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 available 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. Creating a dual boot could be a good solution if you need to run those apps. Read about which apps don't work in Mojave here.
- 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 (or risking it causing problems with the apps and data on your Mac).
How to dual-boot two versions of macOS
So, you want to set up your Mac so you can run two versions of the macOS operating system on it. Your method will depend on which version of macOS you are already running on your Mac. If you are running High Sierra on an SSD or have already installed Mojave this process is much easier because your Mac will be using the new Apple File System APFS.
APFS replaced the old HFS+. APFS has a number of advantages a key one being Space Sharing, which makes it possible to share the available space between the different volumes on your disk - so more space can be made available at anytime, rather than being assigned to the volume when it is created, as is the case with a partition.
So, if you are using APFS you can create a volume as we will show you below, and then just install the new version of the operating system on that volume. You won't need to reformat anything. It couldn't be easier.
- Back up your Mac (because it's always wise to do that before you go on an adventure).
- Use Disk Utility to create a new volume.
- Download the installer for the OS you want (it will have to be a newer version than the one you are running currently - if it isn't then the process will be more complicated and you should read this: How to downgrade to an older version of macOS.
- Install macOS on the new volume you created.
- When you want to boot into the original macOS version press alt/option on startup and you will have the option to enter that volume of your Mac.
We have more detail below about each step, plus you might like to read: How to partition a Mac hard drive or SSD, or create an APFS volume.
If on the other hand you are using an older version of the Mac operating system and don't have APFS, perhaps your Mac has a Fusion Drive and you are running High Sierra and you want to install Mojave on a separate partition, in that case, you will have a slightly more complicated journey that will involve creating a partition. In that case, your steps will run slightly like this:
- Delete things you don't need - make lots of space!
- 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 about each step.
Before you start...
There are two things to do before you start regardless of which version of macOS you are running.
If you want to carve your Mac up so that you can run two versions of the OS you will need space. So before you start get deleting. Remove apps you don't use (here's how to delete apps), delete any files and folders you don't need, copy your huge photo library onto an external drive, etc.
The next important step is to back up. It's always wise to make sure you back up your Mac before you do anything like this, just in case it all goes horribly wrong.
Plus, if you are in an older version of macOS or even Mac OS X, 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 the alternate version of 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. We show you how to create a backup of your Mac here. We also have this guide to using Time Machine, which is Apple's provided software for backing up.
How to install a second macOS on an APFS Volume
The next step is to create an area on your Mac where you can install the second version of the MacOS. As we explained above, this will either be a Volume or a complete Partition.
If you have a Mac with the Apple File System (APFS) then you can follow these steps:
- Open Disk Utility (you can find it in the Utilities folder in Applications, or just press Command + Space and start typing Disk Utility).
- Click the drop-down menu beside the View button in the toolbar and choose Show All Devices. This will make sure you can see the volumes within your disk. It’s likely you have one called Home.
- With the Home volume selected click on the + button above Volume in the menu to create your new Volume.
- Give your new volume a name.
- If you want you can choose to set a storage limit for this volume. To do so, click on Size Option and fill in the Reserve (minimum) and Quota (maximum) options. If you try and assign more space than you have available on your Mac you won't be able to, just leave the options blank.
- Now you can click Add and your new Volume will be added to your Mac.
It's that simple. Now all you need to do is install the other version of macOS on the new volume. This is very simple as long as it's a newer version of the macOS than the one you are currently running...
- Go to the Mac App Store and download the installer for the version of macOS or the macOS beta, just don’t install it yet. Note, if you are after the beta you need to first be signed up as a tester - read about how to get the beta here, and if you are trying to install a version of the Mac OS that is older than the one you already have installed you need to read this: How to install an older Mac OS.
- Once you have downloaded the Installer, you can choose the new volume you created as the destination for the installation.
- Now wait while your Mac installs the new OS on that volume.
- Once it’s done your Mac will open up in the volume with the new OS installed.
- When you are ready to go back to your old version of the OS, just shut down your Mac, and while it starts up keep the Alt/Option key until you see the option to open from your original volume.
How to install a second macOS on a Partition
If you aren't in the APFS world yet, you will need to partition the main hard drive into two separate drives and then install macOS Mojave on one and the other version of MacOS on the other.
If you need to create a partition you will need to wipe your Mac, so as we said above, make sure you make a backup.
The simplest way to create your partition is to do the following:
- Boot macOS into Recovery mode (start up your Mac and hold down the Command and R keys until you see an Apple logo or spinning globe).
- Once in Recovery mode, use Disk Utility to wipe the main hard drive and split it into two partitions.
- Now recover your Time Machine backup into that partition. Remember, you won't be able to recover a backup based on a newer version of macOS than the one you want to be using on this partition.
- Alternatively, you could use the Install option in Recovery to install macOS Mojave (or whichever version you wish to run) on to the main partition.
- Now it's time to install the other version of macOS in partition 2. Follow the steps here to install a second version of macOS, or the beta of the new version of macOS, on to the second partition.