You can run Mojave and Catalina on the same Mac in a dual boot setup and without reformatting or repartitioning your Mac’s storage thanks to APFS, the file formatting system that Apple made ubiquitous with Mojave’s release. Great if you need to use apps that won’t run on Catalina, but still want to use what Catalina has to offer. Here’s how.

About APFS and HFS+

If your apps haven’t been updated to run on macOS Catalina but you wish to enjoy the new features of Catalina, one solution is to install Catalina on the same Mac as Mojave, but in a different Volume. That way you can continue to operate in Mojave with Mojave-compatible apps when you need to, then reboot into Catalina to get used to the new OS. You can do this because Mojave uses APFS, which makes it easier to reconfigure your hard disk or SSD.

APFS was first introduced to the Mac with the release of macOS 10.13 High Sierra in 2017. The new file system is much more robust and thoroughly optimized for modern hardware and specifications, with an eye towards solid state storage like the SSDs. APFS replaces HFS+, which had been the Mac’s file system since the “classic” Mac days – itself built on an even older protocol.

APFS supports logical drives called Volumes, which use the same storage container where free space is available. This is much more efficient than the old method, so long as you have sufficient storage to accommodate more than one installation. So make sure to clear up hard drive space if you need to before installing Mojave and Catalina together.

TIP: Catalina takes advantage of the new APFS volume structure its own way, by creating a read-only system volume. You can read more about what this means in this explainer.

How to create a new Volume on a Mojave Mac

To create a Catalina volume on your Mac, follow these steps.

1) Double-click on Disk Utility in the Utilities folder.

2) Select your Mac hard drive from the sidebar.

3) Click the + button above Volume.

Volume

4) Name your new APFS volume and click Add.

With the new Volume created, you’re on to installing Catalina.

How to install Catalina on a second Volume

1) Download the Catalina installer from the Mac App Store.

2) Double-click on the Catalina installer.

3) Click Continue, click Agree and click Agree again.

Show all disks

4) Click on Show All Disks.

install catalina dual boot

5) Select the new Volume you just created. Then click Install. Do not select the Volume where Mojave is installed, unless you want Catalina to overwrite Mojave.

6) The installation process will begin. Follow the prompts to finish installing Catalina on your new Volume.

The installer will give you the option of migrating data and applications from another Mac. If you wish to bring over your data, settings, or even apps to see how they’ll work in Catalina, simply select the Volume where Mojave remains. But

How to dual boot between Mojave and Catalina

After Catalina is installed, you can switch between Catalina and Mojave using the Startup Disk system preference. Here’s how:

1) Click the Apple menu.

2) Select System Preferences.

3) Click Startup Disk.

4) Click the padlock icon in the lower left corner of the window to unlock the settings. Enter your system password and click Unlock.

5) Select the new Catalina volume and click the Restart button.

Restart

Your Mac will restart in whichever system you choose.

Any questions?

That’s all you need to get started with a dual-boot Mac running both macOS Mojave and Catalina. While it’s not an ideal permanent solution, it’s one way you can run Catalina without disrupting the workflow and tools you’re already dependent on.

Have any questions? Let me know in the comments.