If you've always wanted to partition your Mac's hard drive so you can run a separate operating system — including the launch of macOS Catalina — in tandem with your current one, it's surprisingly easy to do so thanks to Apple's built-in disk utility program. Here's how to partition your Mac.

Feb 04, 2018  Change the size of the partition It's not possible to change the size of the partition after installing Windows, but you can remove the partition and create a new partition of the correct size. Don't try to resize your partition with Windows or a third-party app.

What is a disk partition?

Partitioning your Mac is basically splitting your hard drive into separate, usable systems. It makes it possible to run two separate operating systems on one device, like Windows and macOS or two versions of macOS (like Mojave and Catalina).

Note: If you want to run Windows on your Mac, Apple's Boot Camp assistant will automatically make a partition for you. Here's how to install Windows.

It is important to note that partitioning your hard drive also splits up your available hard drive space. Each partition will take up a portion of your usable storage. So, if you are running low on storage capacity on your hard drive, we don't recommend partitioning.

Before you start

The most important thing to do before making any changes to your hard drive is to back it up. Seriously. Back it up. Please. Time Machine is the easiest way to back up your data if you don't already have another system in place.

Second, make sure you have enough free disk space to properly run a secondary operating system. Shoot for at least 30GB free, though I recommend closer to 50GB if you have it available.

How to create a partition on your Mac

1. Open Finder from your dock.

2. Select Applications.

3. Scroll down and open the Utilities folder.

4. Double-click to open Disk Utility.

5. Select your hard drive in the Disk Utility window. It will be the first drive on the list. It might be named 'Fusion,' or 'Macintosh HD.'
6. Click on the Partition tab. You will be prompted to either add an APFS volume or a Partition.

7. Click Partition.

8. Click the Add partition button it looks like a plus (+) symbol.
9. Change the size of the partition you wish to use by dragging the resize controls. The used space is represented in blue.
10. Name the new partition.
11. Specify which file system format you want to use. If you're running macOS 10.13 or higher, you'll want APFS. If you are running macOS 10.12 or older, you'll want Mac OS Extended.

12. Click apply.

Disk Utility will check the disk and make changes. This will take several minutes.

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How to switch partitions

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You can switch to the new partition, install the current macOS, and then download and install macOS Catalina from there.

1. Click the Apple icon in the upper-left corner of your screen.

2. Select System Preferences from the drop-down menu.

3. Select Startup Disk.

4. Click the Lock in the lower left corner of the window to unlock and make changes.

5. Enter your system admin password.
6. Click OK.
7. Select your partition drive.

8. Click Restart.

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You can also restart your Mac and press the Option Key when you hear the startup chime. This will take you to the Startup Manager and you can select your drive from there.

You will then be asked to install macOS. This will install the latest available macOS onto the partitioned hard drive. You may have to install macOS Mojave before upgrading to macOS Catalina.

How to download macOS Catalina

If macOS Mojave doesn't automatically install on your partitioned hard drive (if it installs macOS High Sierra instead, for example), you can install it from your System Preferences in About this Mac.

After you have macOS Mojave installed, you can follow the instructions to download and install macOS Catalina.

Any questions?

Do you have any questions about installing a partition or downloading a new operating system onto a partitioned drive? Let us know in the comments. If you're having trouble partitioning your hard drive, be sure to check out our forums for help!

Updated September 2019: Updated for macOS Catalina.

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