How to Install Two Versions of macOS on Your Mac
Not many people know that you can have two versions of macOS installed on your Mac at the same time—and without the trouble of partitioning your disk drive. If you have macOS 10.13 or later, then you simply need to create an APFS volume and use that location to install the second macOS version you want.
If you use professional software that often has compatibility issues with recent macOS updates, then this is a fantastic solution as it lets you keep running that software on a stable version of macOS. Other uses include testing software with different macOS versions or using it to safely install a beta versions of macOS.
APFS Makes It Easy to Install Multiple Versions of macOS
In the past, installing two macOS versions on your Mac required creating a dedicated partition on your disk drive and allocating a set amount of storage space to it. But that changed when Apple moved from a file system called Mac OS Extended to using the Apple File System (APFS).
If you have macOS High Sierra (10.3) or later, then by default, your computer will use the APFS format required for this method to work. Using a feature called Space Sharing, you can create multiple volumes within a container and share storage space automatically between them as needed.
All you have to do is create a new volume, download the second macOS version to this location, and then choose the new volume when booting your computer.
It’s easy to set up, a lot more flexible than the old method, and it means you no longer have to choose how much space to permanently assign to a partition, although this option is also available if you want. With that aside, see the steps below for how to install a second version of macOS on your computer.
Can Apple Silicon Macs Run Two Versions of macOS?
Apple Silicon Macs also use APFS volumes, so you can also install a second version of macOS on these computers using the method we’ll describe below. However, one important point to note is that macOS versions older than Big Sur won’t work on silicon Macs due to a change in the processor architecture from the Intel chip to the Apple silicon chips.
While you won’t be able to download older versions of macOS, that still leaves you several options including installing macOS Big Sur, Monterey, beta versions of macOS, and new macOS updates as they are released.
Step 1. Back Up Your Mac
As always, it’s a good idea to back up your Mac in case anything goes wrong during the process. Don’t worry, if you’ve never done it before, there are a couple of easy methods you can choose from for to back up your Mac.
Step 2. Create a New Volume
Start by creating a new APFS volume using Disk Utility on your Mac. You can find this ap by opening Finder and selecting Go > Utilities > Disk Utility from the menu bar.
Once the program is open, press the plus (+) button near the top of the window area, or select Edit > Add APFS Volume from the menu bar. In the dialogue window that appears, enter a new name for the volume and make sure the format is set to APFS. Once you’ve done that click Add.
The new volume should now be listed under the column on the left, alongside your original Macintosh HD disk drive.
Step 3. Download macOS
Next, download the version of macOS that you want to install on your computer. In this case, we wanted to install macOS Monterey on a separate volume. There are also several ways to downgrade to an older version of macOS if you want to head in the other direction.
To download the latest macOS, open the Applications folder on your computer and click on the App Store. Search for the latest macOS version and press Get to start downloading.
You can also check for recent updates by clicking on the Apple logo in the top left corner of your computer screen and selecting About This Mac. Then in the Overview tab press Software Update to check for the latest available updates.
To find older versions of macOS, just search for them on the App Store or on Apple’s website.
Step 4. Choose the Installation Location
Open the macOS installer once it has been downloaded; you can find it in the Applications folder on your computer. When it launches, you will be prompted to select an installation location. Make sure to choose the APFS volume you created in step two, then follow the rest of the installation steps.
It will take some time to install, but once it does, you will have a second macOS version available to use on your Mac. Now you can either switch between macOS versions when you start up your computer or set the new volume as the default disk.
Step 5. Switch Between macOS Versions
To use the new macOS version, or switch between volumes, start by shutting down your Mac.
Next, turn your Mac on while holding down the Option (alt) key on the keyboard. If you have an Apple silicon Mac, just press and hold the power button. You can stop pressing the key once you see the option to choose a startup disk. Using the arrow keys, select the volume that you want to boot up and press Return on the keyboard.
Your computer will now boot up using the version of macOS on the volume you selected.
Step 6. Set a New Default Startup Disk (Optional)
If you think you will use the new macOS version more often, then you can set it as the default startup disk that opens whenever you power on your computer.
Changing the default startup disk is simple, just navigate to System Preferences, then select Startup Disk. From here, click the padlock icon in the bottom left-hand corner and enter your admin password to make changes. Then, simply select the volume you want to use by default at startup and click the padlock icon once again to save your selection.
The Easy Way to Run Two Versions of macOS
With new macOS updates being released every year, it’s hard for software developers to keep programs running smoothly. Using this method, you have a safe option to upgrade your computer while keeping an older version of macOS as you wait for all your apps to be fully compatible.
Running two macOS versions on your computer is also a great solution if you need to test software on different macOS versions, or run a beta macOS.