Concerned virtually updating your Mac to the latest version of macOS? Perhaps y'all aren't certain about running macOS Monterey quite yet, or maybe you want to examination the beta just don't desire to risk messing upwardly your system. Y'all might exist concerned nearly incompatible software or you might only be thinking that yous might hate it and not be able to go back to the macOS you lot are familiar with.

Luckily you don't have to install the OS update on your Mac at all - you can install it on an external drive instead.

Installing the Mac operating system on an external bulldoze is the safest way to get a skilful look at a new OS without changing anything on your Mac. It'll go out your current configuration intact and allow you to play around with Monterey or try out the beta of the side by side version of macOS.

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

  1. Prepare the external drive for the installation using Disk Utility.
  2. Get the macOS install files - we'll evidence you how.
  3. Install macOS on the external bulldoze.
  4. Run macOS on the external drive past pressing Alt/Selection at first up on an Intel-powered Mac, or pressing and property the on switch on an M1 Mac.

What you need

If yous want to run macOS on an external drive you will need a few things including a bulldoze with a good amount of storage available.

Make sure that you opt for flash storage because Apple's APFS (Apple file system) is optimized for SSD and the computer will be sluggish if you try to boot from a hard drive. It'south likewise worth investing in a USB C or Thunderbolt 3 drive every bit this will offer the fastest connectedness.

You can get concur of a USB flash stick pretty cheaply, such as this San Disk USB Blazon-C drive with 256GB for £30.93 (RRP £59.99). It'due south a bit harder to observe a Thunderbolt powered SSD, and unfortunately they are a lot more expensive. One instance is the Samsung X5 Thunderbolt iii 1TB SSD, currently £273.98 from Amazon (RRP £344.99).

If you want to use the external installation as if you are running information technology on your Mac we advise you get the biggest USB C/Thunderbolt 3 drive you can afford. For more ownership advice, take a look at our guide to the best external drives for Mac.

Troubleshooting problems with the M1 Mac

Before nosotros move on to how you can create this external installation of macOS we will mention some issues people had when trying to create such an installation for an M1 Mac.

After the first M1 Macs launched in 2022 information technology emerged that there was a problem with the USB interface. As a result some users encountered problems trying to install macOS on and booting from SSDs connected via USB. This upshot was quickly addressed in Big Sur 11.0.1, improved further in eleven.1 and refined over again in 11.two. The problem has now been addressed by Apple'southward developers, merely if y'all find it affects you lot we propose that you lot do the post-obit:

  • Try a different port. For some it has worked to install on a disk connected via USB-A connector, simply non USB-C, while the situation has been vice versa for others.
  • Another solution is to use a bulldoze that uses Thunderbolt rather than USB (the port looks the same, merely the standard is different). It should be connected directly to the estimator, not via a dock. That bulldoze will need a good amount of space (back when we started running Mojave beta on a 32GB stick nosotros found information technology wasn't plenty once we started using iCloud Desktop and other features that meant that our data started beingness downloaded).

Another effect worth flagging is that if you were hoping to utilize this kick bulldoze to run older versions of macOS on M1 Macs sadly it isn't possible as the M1 Mac tin can merely run the ARM version of Big Sur.

Install MacOS on a external drive

Step 1: Prepare the drive for installation

Follow these instructions to prepare your external drive - note that in that location may be some slight changes to the process if you wish to install the macOS Monterey or the latest beta.

  1. Connect the external drive to your Mac.
  2. Launch Disk Utility (press Cmd + spacebar and beginning to type Disk Utility).
  3. Before this side by side pace - if you are running High Sierra or afterward you lot will need to click on the View driblet downwardly below the shut/minimise buttons. Choose Prove All Devices from the options.  Now you lot will see the root drive in add-on to the external volume below it. Show all Disk Utility
  4. Select the External bulldoze in the sidebar (the next step won't work if you merely select the volume - in the screenshot above you would need to select the SanDisk, not the NO Name).
  5. Click on Erase (yous demand to erase the drive so yous can reformat information technology properly).
  6. Give your drive a name such as "macOS Big Sur" or "USB".
  7. Cull Mac OS Extended (Journaled) as the Format.
  8. Choose GUID Partition Map as the Scheme. Format options Disk Utility
  9. Click on Erase.
  10. Wait while Disk Utility creates the partition and sets up the drive (this tin have a few minutes).
  11. Then click Done.

At present you will encounter that your external storage has been renamed with the name you choose and it volition be ready for yous to install the macOS on it - but there is something else you need to do outset.

Pace 2: Become the macOS install files

This footstep volition depend on whether you desire to run a macOS beta, a total version of macOS, or fifty-fifty an older Mac OS X.

Whether you desire to become the macOS Monterey or the latest beta installation files the process to exist similar to that detailed below. When Monterey becomes available to download on 25 October 2022 you should exist able to get the installation files via Software Update or the Mac App Store.

Here's how to become the macOS Big Sur or Catalina installer:

  1. To download the macOS Big Sur installer click here to get to the Big Sur folio on the Mac App Store. To download the macOS Catalina installer click on this link to the Mac App Store.
  2. Click on Get to download the installer.
  3. Software Update will search and then, if yous are already running Large Sur (or Catalina), if will ask you to confirm that you do want to download macOS Large Sur (or Catalina).
  4. Click on Download.

Remember that yous merely want to download the software, not install it, at this stage.

If information technology'southward a full version of an older version of  macOS you are afterward, nosotros explicate how to get the installation files for macOS hither.

If you are later on a beta of macOS, you will demand to sign up for the beta on your Mac and download the beta files. Once you take the files you'll want to install them on the external drive rather than your Mac, so be careful. Nosotros have a complete guide to getting the macOS beta here. The beta files are about 12GB.

Step 3: Install macOS on the external drive

At present to install the beta or alternative version of the Mac operating organisation on your external drive.

  1. Open a finder window, go to Applications and observe the Catalina or Large Sur installer (or whichever version of macOS y'all want to run). You can as well detect information technology past using Spotlight (press Command + spacebar and start typing the name of the Bone)
  2. Click on the installer.
  3. A window should open (check the Dock if not). It will invite yous to fix up the installation of macOS Monterey (or any) click Continue.
  4. Concur to the software licence agreement.
  5. Side by side, and this is important, click on Prove All Disks. Do not click on Home as you don't want to install on your main drive.
  6. Click on the external bulldoze.
  7. Click Install.

Await while the version of macOS installs on the drive. This procedure may have a while - if it tells you it volition have 10 minutes information technology's lying.

Notation: This will not work if you didn't set your external drive up correctly as a GUID Partition every bit per the steps higher up.

Step 4: Run macOS on the external drive

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

Either:

  1. Open Arrangement Preferences > Startup Disk.
  2. Select the external drive y'all wish to use to start upwardly the Mac and click Restart.

Or:

  1. Hold downward Option/Alt during startup on an Intel-powered Mac, or press and hold the on button on an M1 Mac until you see the starting time upward options.
  2. Choice the drive you lot wish to use to first up the Mac.

One time yous have installed the macOS you want on the drive it should be like shooting fish in a barrel to install subsequent updates there via System Preferences.

For more than communication about installing macOS or Mac OS Ten read How to update the Mac operating system and How to install old versions of OS 10 on a Mac.