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Installing a new Mac operating system can be a daunting task, which may lead to software incompatibilities, slow performance, or other issues. The best way to avoid such issues is to install the new operating system on an external hard drive rather than your Mac’s internal drive.
This tutorial will guide you through the process of installing macOS on an external drive, which is the safest way to explore a new operating system without making any changes to your Mac’s existing configuration.
What You Need
To start with, you need a fast drive, preferably with USB-C or Thunderbolt 3 interface that offers the fastest connection to your Mac. If not, at least go for flash storage. The drive must have at least 12 GB of space and bigger if possible, especially if you want to use the remote install. Check our guide to find the best external drives for Mac.
Step 1 – Prepare for the Installation
Follow these instructions to set up your external drive:
- Connect the external hard drive to your Mac.
- Launch Disk Utility (press Cmd + Spacebar and begin typing Disk Utility).
- Before the next step, if you are using High Sierra or later, click on the Show drop-down list under the lower buttons and choose Show All Devices. You’ll then see the external root drive next to the volume under it.
- Select the root drive in the sidebar, and not just the volume.
- Click on “Erase”.
- Choose “Mac OS Extended (Journaled)” as the format.
- Choose “GUID partition map” as the scheme.
- Give a name to your disk, such as “macOS Catalina” or “USB”.
- Click on “Erase”.
- Wait while Disk Utility creates the partition and sets up the disk (this may take a few minutes).
- Click “Done” when it finishes.
Step 2 – Download the macOS Installation Data
The downloading process depends on whether you want to use the beta or a full version of macOS or even an older Mac OS X. If you want to download the Catalina installer, follow these instructions:
Open System Preferences > Software Update. Your Mac will search for the latest software before offering to download it. Alternatively, you may click this link to go to the Catalina page in the Mac App Store. Note that at this stage, you only need to download the software and not install it.
If you want to download the full version of an older macOS, follow the instructions provided in the guide. To download the Catalina beta, you need to follow these steps:
- Register as a developer or for the public beta program.
- After completing the above step, download the Public Beta Access Utility (or Developer Beta Access Utility) from the Apple website.
- Open the Beta Access Utility DMG file in your Downloads folder and click “macOSPublicBetaAccessUtility.pkg” to install it (it’s 215 KB).
- You may need to enroll your Mac. To check if your Mac is enrolled, open System Preferences > Software Updates (in earlier versions of MacOS, App Store). If your Mac is enrolled, you will see “Your computer is set to receive beta software updates.”
- Once the Beta Access Utility is installed, the Software Update tool will open, and the beta will download. (If you’re using an older version of MacOS, you’ll be redirected to a Catalina page in the Mac App Store. You’ll not see this if you’re not registered and use the access utility). Click “Download” and wait while it downloads to your Mac. The download may take some time due to the file being over 5 GB, but you should be able to continue working while the download is in progress.
- Once the download completes, your Mac will start it up. WARNING: You don’t intend to install it on your Mac, so DO NOT CLICK CONTINUE. Exit the installer instead.
- You can find the installer ‘Install macOS Catalina Beta’ on your Applications folder.
Step 3 – Install macOS on the External Drive
Now you can install the beta or another version of the Mac operating system on your external drive by following these steps:
- Open a search window, go to Applications, and find the Catalina Beta installer (or whatever version of macOS you want to use).
- Click on the installer.
- In the main window, click ‘Continue’ to initiate the installation of the macOS Catalina Beta (or whatever version you choose).
- Agree to the software license agreement.
- Click on “Show All Disks” (NOT Home), as you don’t want to install on your main drive.
- Click on the external drive and click “Install”.
Wait while the macOS is installed on the disk. This process may take some time – if it tells you it takes 10 minutes, it’s lying. Note: This will not work if you have not set up your external drive as a GUID partition.
Step 4: Run macOS on the External Drive
There are two ways to run the version of macOS from your external drive:
- Launch System Preferences > Startup Disk.
- Select the external drive you want to use to start up the Mac, and click “Restart”.
Or:
- Hold down Option / Alt during startup.
- Select the drive you want to use to boot the Mac.
With this guide, you can now install a new macOS on an external drive and explore the new features and functionalities with ease.
FAQs
1. Is it safe to install a new macOS on an external drive?
Yes, it is safe to install a new MacOS on an external drive. This method avoids any possible software incompatibilities on your Mac’s internal drive.
2. Do I need a fast external drive to install MacOS?
It’s recommended that you use a fast external drive such as a USB-C or Thunderbolt 3 drive for installing macOS as it offers the fastest connection.