How to install macOS on an external drive

Are you worried about having to update your Mac to the latest version of macOS? Maybe you’re not sure if you want to use macOS Sequoia yet, or maybe you want to test the beta without risking messing up your system. Maybe you’re worried about incompatible software, or maybe you just think you might hate it and won’t be able to go back to the macOS you know.

Fortunately, you don’t need to install the operating system update on your Mac. You can install it on an external drive.

Installing the Mac operating system on an external drive is the safest way to get a good taste of a new operating system without changing anything on your Mac. This will leave your current setup intact and allow you to play around with the beta version of the next version of macOS.

In this tutorial, we explain how to run macOS from an external drive in four easy steps:

1. Prepare the external drive for installation using Disk Utility.
2. Get the macOS installation files. We’ll show you how.
3. Install macOS on the external drive.
4. Run macOS on the external drive by pressing Alt/Option at startup on an Intel-based Mac, or by pressing and holding the power button on an M1 or M2 series Mac.

What you need

If you want to run macOS on an external drive, you’ll need a few things, including a drive with a good amount of available storage.

You can use an external hard drive or SSD, and SSDs offer faster boot times than HDDs. It’s also worth investing in a USB-C or Thunderbolt drive, as these will offer the fastest connection.

You can get a USB flash drive for a pretty affordable price, like this 128GB San Disk USB Type-C drive for $24/£16.49. It’s a little harder to find a Thunderbolt-powered SSD, and unfortunately, they’re a lot more expensive. Check out our roundup of the best SSDs . If you want to use the external setup as if you were running it on your Mac, we suggest buying the biggest USB-C/Thunderbolt drive you can afford.

For more buying advice, check out our guide to the best external drives for Mac for cheaper non-SSD options.

Troubleshooting Problems with M-Series Macs

Before we move on to how you can create this external macOS installation, we will mention some issues that people have encountered while trying to create such an installation for an M-series Mac.

After the first M1 Macs were launched in 2020, it became apparent that there was an issue with the USB interface. As a result, some users experienced issues installing macOS and booting from USB-connected SSDs. This issue was quickly fixed in an OS update, but if you find that it affects you, we suggest you do the following:

• Try a different port. For some, installing to a drive connected via USB-A worked, but not via USB-C, while for others it was the opposite.
• Another solution is to use a drive that uses Thunderbolt rather than USB (the port is the same, but the standard is different). It should be connected directly to the computer, not via a docking station. This drive will need a fair amount of space (back when we started running the Mojave beta on a 32GB drive, we found that wasn’t enough once we started using iCloud Desktop and other features that meant our data started downloading).

Another issue worth noting is that if you were hoping to use this boot drive to run older versions of macOS on M1 Macs, that’s unfortunately not possible as the M1 Mac can only run the ARM version of Big Sur.

Step 1: Prepare the drive for installation

Follow these instructions to prepare your external hard drive. Note that there may be slight changes to the process if you want to install macOS Ventura or the latest macOS beta.

1. Connect the external drive to your Mac.
2. Launch Disk Utility (press Cmd + Spacebar and start typing Disk Utility).
3. Before this next step: If you are using High Sierra or later, you will need to click on the View drop-down menu. Choose Show all devices from the options. You will now see the root drive in addition to the external volume below it.

Foundry

Foundry

Foundry

4. Select the external drive in the sidebar (the next step will not work if you only select the volume – for example, in the screenshot above, you need to select the specific storage, not Untitled).
5. Click on To erase (you must erase the drive to be able to reformat it properly).
6. Give your drive a name such as “macOS Sequoia” or “USB”.
7. Choose APFS like the format.

8. Click on To erase.
9. Wait while Disk Utility creates the partition and configures the drive (this may take a few minutes).
10. Then click Do.

You will now see that your external storage has been renamed to the name you chose and will be ready for you to install macOS on it. But there is something else you need to do first.

Step 2: Retrieve macOS installation files

This step will depend on whether you want to run a beta version of macOS, a full version of macOS, or even an older Mac OS X.

Whether you want to get the installation files for macOS Sequoia or the latest beta, the process is similar to the one detailed below. When macOS version 2024 is available for download, you should be able to get the installation files through Software Update or the Mac App Store.

Here’s how to get the macOS Sequoia installer:

1. To download the macOS installer, click here to go to the Ventura page on the Mac App Store.
2. Click Get to download the installer.
3. Software Update will perform a check and, if you are already running Ventura, it will ask you to confirm that you want to download macOS Ventura.
4. Click Download.

Remember that you just want to download the software, not install it, at this point.

If you’re looking for a full version of an older version of macOS, we explain how to get the installation files for macOS here.

If you want to get a macOS beta, you’ll need to sign up for the beta on your Mac and download the beta files. Once you have the files, you’ll need to install them on the external hard drive rather than your Mac, so be careful. We have a full guide to getting the macOS beta here . The beta files are about 12GB.

Step 3: Install macOS on the external drive

Now install the beta or alternative version of the Mac operating system on your external drive.

1. Open a Finder window, go to Applications and search for the Sequoia installer (or whatever version of macOS you want to run). You can also find it using Spotlight (press Command+Spacebar and start typing the name of the operating system)
2. Click on the installer.
3. A window should open (check the Dock if it doesn’t) that will prompt you to set up the macOS Sequoia (or other) installation and click Continue.
4. Accept the software license agreement.

5. Following-it’s important–click on Show all disksDo not click Home as you do not want to install to your primary drive.
6. Click on the external drive.
7. Click Install.

Wait while the macOS version is installed on the disk. This process may take some time, it always takes longer than the estimated time.

Note: This will not work if you have not correctly configured your external drive as a GUID partition according to the steps above.

Step 4: Run macOS on the external drive

There are two ways to run the macOS version from your external drive

Either:

1. Open System Preferences > Boot Disk Or System Settings > General > Boot Disk.
2. Select the external drive you want to use to boot the Mac and click Restart.

Or:

1. Hold down the Option/Alt key during startup on an Intel-based Mac, or hold down the power button on an M-series Mac until the startup options appear.
2. Choose the drive you want to use to start the Mac.

Once you’ve installed the desired macOS on the drive, it should be easy to install future updates via System Preferences.

For more tips on installing macOS or Mac OS X, read How to update your Mac operating system and How to install older versions of OS X on a Mac.