Install Big Sur From External Drive

Concerned about updating your Mac to the latest version of macOS? Possibly y’all aren’t sure nearly running macOS Monterey quite yet, or maybe you lot want to test the beta simply don’t want to risk messing up your system. Yous might be concerned about incompatible software or you lot might just be thinking that you might hate information technology and not be able to become dorsum to the macOS you are familiar with.

Luckily you don’t have to install the Bone update on your Mac at all – yous can install it on an external bulldoze instead.

Installing the Mac operating organization on an external drive is the safest fashion to get a good expect at a new OS without changing annihilation on your Mac. It’ll leave your current configuration intact and allow y’all to play around with Monterey or try out the beta of the next version of macOS.

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

  1. Prepare the external bulldoze for the installation using Deejay Utility.
  2. Get the macOS install files – nosotros’ll testify you how.
  3. Install macOS on the external drive.
  4. Run macOS on the external drive by pressing Alt/Option at start upwards on an Intel-powered Mac, or pressing and holding the on switch on an M1 Mac.

What y’all need

If you want to run macOS on an external drive you will demand a few things including a drive with a skillful amount of storage available.

Make certain that you opt for flash storage because Apple’south APFS (Apple file system) is optimized for SSD and the figurer volition be sluggish if you try to kick from a hard drive. Information technology’s also worth investing in a USB C or Thunderbolt 3 drive every bit this will offer the fastest connection.

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

If you desire to apply the external installation equally if you are running it on your Mac nosotros suggest you become the biggest USB C/Thunderbolt three drive y’all can afford. For more than ownership advice, take a wait at our guide to the all-time external drives for Mac.

Troubleshooting problems with the M1 Mac

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

Later on the offset M1 Macs launched in 2020 it emerged that in that location was a trouble with the USB interface. Every bit a outcome some users encountered problems trying to install macOS on and booting from SSDs continued via USB. This issue was quickly addressed in Big Sur 11.0.1, improved further in and refined again in eleven.2. The trouble has now been addressed past Apple’s developers, but if you find it affects you nosotros suggest that you exercise the post-obit:

  • Try a different port. For some it has worked to install on a disk connected via USB-A connector, but 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, but the standard is different). Information technology should be connected straight to the computer, not via a dock. That drive will need a good corporeality of infinite (back when we started running Mojave beta on a 32GB stick we plant information technology wasn’t plenty once nosotros started using iCloud Desktop and other features that meant that our data started being downloaded).

Some other outcome worth flagging is that if you were hoping to utilise this boot drive to run older versions of macOS on M1 Macs sadly information technology isn’t possible as the M1 Mac tin can only run the ARM version of Big Sur.

Step 1: Prepare the drive for installation

Follow these instructions to prepare your external drive – note that there may exist 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 blazon Disk Utility).
  3. Before this next step – if you are running High Sierra or subsequently you will need to click on the View drop down below the close/minimise buttons. Choose Show All Devices from the options.  Now you lot will see the root drive in addition to the external volume below it.
    Show all Disk Utility
  4. Select the External drive in the sidebar (the adjacent step won’t work if you only select the book – in the screenshot in a higher place you would demand to select the SanDisk, not the NO NAME).
  5. Click on Erase (yous need to erase the drive so yous tin reformat it properly).
  6. Give your drive a name such every bit “macOS Large Sur” or “USB”.
  7. Choose 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 Deejay Utility creates the sectionalisation and sets upwardly the drive (this tin can take a few minutes).
  11. Then click Done.

Now you will come across that your external storage has been renamed with the name you choose and it volition be gear up for y’all to install the macOS on it – simply at that place is something else y’all need to do get-go.

Step 2: Get the macOS install files

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

Whether you want to get 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 2021 you should exist able to get the installation files via Software Update or the Mac App Shop.

Here’southward how to get the macOS Large Sur or Catalina installer:

  1. To download the macOS Large Sur installer click hither to get 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 volition search so, if y’all are already running Big Sur (or Catalina), if will ask yous to ostend that you do want to download macOS Big Sur (or Catalina).
  4. Click on Download.

Remember that you just want to download the software,
install it, at this phase.

If it’s a full version of an older version of  macOS you are after, we explain how to get the installation files for macOS hither.

If you are later a beta of macOS, y’all will need to sign up for the beta on your Mac and download the beta files. Once you take the files you’ll desire to install them on the external drive rather than your Mac, then exist careful. We accept a consummate guide to getting the macOS beta here. The beta files are almost 12GB.

Stride 3: 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 Big Sur installer (or whichever version of macOS you lot want to run). You can too find information technology past using Spotlight (printing Command + spacebar and start typing the name of the OS)
  2. Click on the installer.
  3. A window should open (bank check the Dock if not). Information technology volition invite you to set up the installation of macOS Monterey (or whatsoever) click Go on.
  4. Agree to the software licence agreement.
  5. Next,
    and this is of import, click on Show All Disks. Do not click on Dwelling as you don’t desire to install on your master bulldoze.
  6. Click on the external drive.
  7. Click Install.

Wait while the version of macOS installs on the drive. This procedure may take a while – if information technology tells you it will take x minutes it’s lying.

Note: This volition not work if y’all didn’t set your external drive up correctly every bit a GUID Segmentation as per the steps above.

Step 4: Run macOS on the external bulldoze

In that location are two ways to run the version of macOS from your external drive


  1. Open Organisation Preferences > Startup Disk.
  2. Select the external bulldoze you wish to use to start up the Mac and click Restart.


  1. Hold down Choice/Alt during startup on an Intel-powered Mac, or press and hold the on push on an M1 Mac until you encounter the start upward options.
  2. Pick the drive you wish to employ to start upwards the Mac.

One time you have installed the macOS you want on the drive information technology should exist easy to install subsequent updates there via Organization Preferences.

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