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.
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).
Jun 19, 2018 Check Your Disk to See What is Taking Up Space and Find Large Files. To free up disk space, it’s helpful to know exactly what is using disk space on your Mac. A hard disk analysis tool like Disk Inventory X will scan your Mac’s hard disk and display which folders and files are using up the most space. You can then delete these space hogs to.
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
- Open Finder from your dock.
- Select Applications.
- Scroll down and open the Utilities folder.
- Double-click to open Disk Utility.
- 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.'
- Click on the Partition tab. You will be prompted to either add an APFS volume or a Partition.
- Click Partition.
- Click the Add partition button it looks like a plus (+) symbol.
- Change the size of the partition you wish to use by dragging the resize controls. The used space is represented in blue.
- Name the new partition.
- 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.
- Click apply.
Disk Utility will check the disk and make changes. This will take several minutes.
How to switch partitions
You can switch to the new partition, install the current macOS, and then download and install macOS Catalina from there.
- Click the Apple icon in the upper-left corner of your screen.
- Select System Preferences from the drop-down menu.
- Select Startup Disk.
- Click the Lock in the lower left corner of the window to unlock and make changes.
- Enter your system admin password.
- Click OK.
- Select your partition drive.
- Click Restart.
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.
macOS Catalina
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By default, your Mac starts up from its built-in hard disk, but a startup disk can be any storage device that contains an operating system compatible with your Mac. For example, if you install macOS on an internal or external drive, your Mac can recognize that drive as a startup disk. You can then follow the steps in this article to start up from it.
Use Startup Disk preferences
When you use Startup Disk preferences to select a startup disk, your Mac starts up from that disk until you choose a different one.
- Choose Apple () menu > System Preferences, then click Startup Disk.
- Click and enter your administrator password.
- Select your startup disk, then restart your Mac.
If you see a message that your security settings do not allow this Mac to use an external startup disk, check the External Boot setting in Startup Security Utility.
Use Startup Manager
When you use Startup Manager to select a startup disk, your Mac starts up from that disk once, then returns to using the disk selected in Startup Disk preferences.
- Press and hold the Option key immediately after turning on or restarting your Mac.
- Release the Option key when you see the Startup Manager window.
If your Mac is protected by a firmware password, you can release the key when you're asked to enter the password. - Select your startup disk, then click the arrow under its icon, or press Return.
If you press and hold the Control key during this step, your selection is saved in Startup Disk preferences, so it persists until you change it.
If your Mac is using OS X Lion 10.7.3 or later, you can also use this method to start up from your Time Machine backup disk. Startup Manager identifies your Time Machine backup as ”EFI Boot.”
If you can't select your startup disk or start up from it
Check for these possibilities if you can't see your disk in Startup Disk preferences or Startup Manager, or your Mac won't start up from it.
Check for a valid operating system on the startup disk
Make sure that your startup disk is using a version of macOS that's compatible with your Mac. You might need to reinstall macOS on that disk.
Check startup security settings
If you're using a Mac that has the Apple T2 Security Chip, check the settings in Startup Security Utility. These settings determine whether your Mac can start up from another disk.
Check for Option ROM firmware
If you're in Startup Manager and can't see your startup disk, press Option-Shift-Command-Period. If that works, do this each time you want to start up from the device or from a startup disk connected to it.
To enhance system security, Mac computers with up-to-date software don’t show devices that have Option ROM firmware until you press these keys in Startup Manager to load the firmware. On Mac models from early 2015 or earlier, you can disable this security feature to load Option ROM firmware automatically. This removes an important protection against potential unauthorized access to your Mac by other people with physical access to it.
- Open the Terminal app, which is in the Utilities folder of your Applications folder.
- Type
sudo nvram enable-legacy-orom-behavior=1
, then press Return.
To undo this command, entersudo nvram -d enable-legacy-orom-behavior
.
If you're using a firmware password on your Mac, the ability to load Option ROM firmware automatically or manually is disabled as an additional security protection. If you want to remove this additional protection but keep your firmware password:
- Open the Terminal app, which is in the Utilities folder of your Applications folder.
- Type this command, then press Return:
sudo firmwarepasswd -setmode command -allow-oroms
To undo this command, entersudo firmwarepasswd -setmode command
. - Type the administrator password for your user account, then press Return.
- Type your firmware password, then press Return.
- Restart your Mac.