Concerned well-nigh updating your Mac to the latest version of macOS? Perhaps you aren't sure nigh running macOS Monterey quite all the same, or maybe you want to test the beta but don't desire to hazard messing up your organization. Y'all might exist concerned nigh incompatible software or you might merely be thinking that you might hate it and non be able to go back to the macOS you are familiar with.

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

Installing the Mac operating system on an external drive is the safest way to get a good look at a new Bone without changing anything on your Mac. It'll leave your current configuration intact and allow y'all to play around with Monterey or endeavour out the beta of the next version of macOS.

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

  1. Prepare the external drive for the installation using Deejay Utility.
  2. Go the macOS install 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 start up on an Intel-powered Mac, or pressing and holding the on switch on an M1 Mac.

What you demand

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

Brand sure that you opt for flash storage because Apple's APFS (Apple file system) is optimized for SSD and the calculator will be sluggish if y'all attempt to kick from a difficult drive. It'south also worth investing in a USB C or Thunderbolt 3 bulldoze equally this volition offer the fastest connectedness.

You can get hold of a USB flash stick pretty cheaply, such as this San Deejay USB Type-C drive with 256GB for £30.93 (RRP £59.99). It's a flake harder to find a Thunderbolt powered SSD, and unfortunately they are a lot more expensive. One example is the Samsung X5 Thunderbolt 3 1TB SSD, currently £273.98 from Amazon (RRP £344.99).

If you want to use the external installation as if you are running it on your Mac we suggest y'all go the biggest USB C/Thunderbolt 3 drive you tin can beget. For more than ownership advice, accept a look at our guide to the best external drives for Mac.

Troubleshooting problems with the M1 Mac

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

After the first M1 Macs launched in 2022 it 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 consequence was apace addressed in Large Sur 11.0.1, improved further in 11.1 and refined over again in eleven.two. The problem has now been addressed by Apple tree's developers, just if you notice it affects you we suggest that y'all do the following:

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

Another issue worth flagging is that if yous were hoping to use this kick drive to run older versions of macOS on M1 Macs sadly it isn't possible as the M1 Mac can only run the ARM version of Big Sur.

Install MacOS on a external drive

Stride one: Prepare the bulldoze for installation

Follow these instructions to ready your external bulldoze - annotation that at that place may be some slight changes to the process if y'all 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 start to type Disk Utility).
  3. Before this next step - if you are running High Sierra or later you will need to click on the View drop down below the shut/minimise buttons. Choose Show All Devices from the options.  Now y'all will come across the root bulldoze in addition to the external book below it. Show all Disk Utility
  4. Select the External drive in the sidebar (the next step won't work if you only select the volume - in the screenshot in a higher place you would need to select the SanDisk, not the NO Proper name).
  5. Click on Erase (you need to erase the drive so you tin can reformat it properly).
  6. Requite 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. Await while Disk Utility creates the partition and sets upwards the drive (this can accept a few minutes).
  11. Then click Done.

Now yous will come across that your external storage has been renamed with the name y'all choose and it volition be fix for you to install the macOS on it - only there is something else you demand to do first.

Stride 2: Get the macOS install files

This pace will depend on whether you want to run a macOS beta, a full version of macOS, or fifty-fifty an older Mac Os X.

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

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

  1. To download the macOS Big Sur installer click here to become to the Big Sur page on the Mac App Store. To download the macOS Catalina installer click on this link to the Mac App Shop.
  2. Click on Get to download the installer.
  3. Software Update will search and then, if y'all are already running Big Sur (or Catalina), if volition ask you lot to confirm that you lot do want to download macOS Big Sur (or Catalina).
  4. Click on Download.

Remember that you just want to download the software, non install information technology, at this stage.

If it's a full version of an older version of  macOS you are after, we explicate how to get the installation files for macOS here.

If you are after a beta of macOS, you volition need to sign up for the beta on your Mac and download the beta files. One time you accept the files you'll desire to install them on the external drive rather than your Mac, so be careful. We have a consummate guide to getting the macOS beta here. The beta files are about 12GB.

Step iii: Install macOS on the external drive

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

  1. Open a finder window, get to Applications and find the Catalina or Large Sur installer (or whichever version of macOS y'all desire to run). You can also detect it by using Spotlight (printing Command + spacebar and get-go typing the proper name of the Bone)
  2. Click on the installer.
  3. A window should open (check the Dock if not). Information technology will invite you to prepare up the installation of macOS Monterey (or whatever) click Continue.
  4. Hold to the software licence agreement.
  5. Next, and this is of import, click on Show All Disks. Do not click on Dwelling as y'all don't want to install on your main drive.
  6. Click on the external drive.
  7. Click Install.

Await while the version of macOS installs on the drive. This process may take a while - if it tells you it will have 10 minutes it'due south lying.

Annotation: This will non piece of work if you didn't set your external drive upward correctly as a GUID Sectionalisation as per the steps above.

Step 4: Run macOS on the external drive

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

Either:

  1. Open up System Preferences > Startup Disk.
  2. Select the external drive you wish to utilise to first up the Mac and click Restart.

Or:

  1. Hold down Option/Alt during startup on an Intel-powered Mac, or printing and concur the on button on an M1 Mac until you see the commencement up options.
  2. Option the bulldoze you wish to employ to start up the Mac.

One time you have installed the macOS you lot want on the drive it should exist easy to install subsequent updates there via System Preferences.

For more advice about installing macOS or Mac Os X read How to update the Mac operating arrangement and How to install onetime versions of OS X on a Mac.