Install macOS Big Sur and Catalina in parallel without a partition

Thanks to the APFS file system, it is very easy on the Apple Mac to install two operating systems in parallel on one hard drive - and that without partitions. In the past, hard disks had to be broken down into individual virtual parts (partitions), today it is sufficient to set up a so-called APFS volume. How you do it, how you can use it to install macOS Big Sur and Catalina in parallel, and how you choose which operating system should boot when the Apple Mac starts, you will find out everything in this guide.

Here you will find step-by-step instructions to install macOS Big Sur and Catalina in parallel without a partition. With an APFS volume you can easily use two boot systems on the Apple Mac.

Here you will find step-by-step instructions to install macOS Big Sur and Catalina in parallel without a partition. With an APFS volume you can easily use two boot systems on the Apple Mac.

Same procedure as with macOS Mojave and Catalina

Last year I already gave you instructions on how to use the APFS file system on the Mac's startup volume for the parallel installation of two operating systems. You can find them under this title: Install macOS Catalina without a partition parallel to Mojave. If, instead of macOS 10.14 and 10.15, you plan to double use the Mac hard drive with macOS 10.15 and macOS 11.0, you basically proceed in the same way as a year ago. The advantages are very clear: In contrast to a partition, an APFS volume simply has to be added to the existing list. No storage space has to be reserved for this, as it grows dynamically and only uses the storage space that it really needs.

Install macOS Big Sur and Catalina in parallel

So if you want to install macOS Big Sur and Catalina in parallel without a partition, then proceed as follows:

  1. Opens the Disk Utility (from the Utilities folder, Launchpad, or Spotlight)
  2. Checks whether your hard drive (probably “Macintosh HD”) is an APFS volume
  3. If so, click on the "+" (plus sign) above the term "Volume"
  4. Enter the name for the new volume, for example "Big Sur"
  5. Leave the format at APFS and confirm the creation of the new storage compartment

Once that's done, you've already reserved the storage location for the new operating system. To install macOS 10.15 Big Sur at the same time with an existing macOS 11.0 Catalina, simply work through the following step-by-step instructions:

  1. Start the macOS Big Sur installer from your hard drive
  2. On the overview of the installation locations (at least) the current volume is now displayed
  3. Click on "Show all volumes ..." to also display the newly created volume
  4. If this appears in the overview (or was it seen before), select it as the destination
  5. Install macOS Big Sur on the new APFS volume

Boot selection: Which operating system should the Mac start up with?

So now you have two operating systems on the hard drive of your Apple computer. The question arises as to which one should start with. You can easily set this via the system settings. Simply click on the Mac menu ( symbol) in the top left of the menu bar and then on "System Preferences ...". Then click on "Startup Disk". After the installation described above, you should see a volume with "macOS, 10.15.7" and one with "macOS, 11.0.1" (version status: 16.11.2020). Select one of them and restart your Mac - if necessary or to try it out.

Spontaneous selection: Select the macOS version when the Mac starts up

If you don't want to first select the primary operating system and then start the secondary from it, there is a short shortcut. Appropriately, the so-called option key is used for this. This is also called option or old and may have the symbol ⌥ printed on it. If you hold down this key immediately after turning on the Mac, you will get to the startup disk selection. This avoids the problem that switching from one macOS to another during operation always involves a restart. A virtual execution, such as Windows via Parallels Desktop or Linux via a virtual machine, is not offered by Apple.

More articles on macOS 11.0: Installation, Problems and Solutions

Now you can install macOS 11.0 Big Sur and macOS 10.15 Catalina in parallel without a partition. Thanks to Apple's own file system APFS (Apple File System), this is very easy, which already helped with the Catalina installation next to Mojave last year. If you want to take a closer look at Big Sur, I can recommend these posts here in the blog:


Did you like the article and did the instructions on the blog help you? Then I would be happy if you the blog via a Steady Membership or at Patreon would support.


  1. peter bird says:

    Sounds good. Can I remove one of the volumes if necessary?

  2. Dirk says:

    Tip: If you have enough storage space, you can use it to "mirror" your system and thus do a "Big Sur trial update" on a copy of your current system.

    To do this, start the recovery and specify the newly added hard drive there. Then select the migration assistant when restarting after the installation and specify the original hard drive as the source. Then run the Big Sur update on the copy, relaxed and without sweating.

    This is how I did it on my MacBook Pro 16 ′ (4TB) after spending hours in vain with Copy Cloner and external SSDs. Unfortunately, I realized much too late that it was so easy and, above all, quick!

    PS: The update result surprised me: Everything ran straight away, no problems with apps etc. and Big Sur feels much better. So after extensive tests I simply deleted the copy (hard drive) and then updated Bug Sur on the "original". A step that I would otherwise have taken a few months from now.

    • Jen Kleinholz says:

      Hello Dirk! Great, the migration assistant is also a good way to make a backup, because Carbon Copy Cloner currently cannot make bootable backups. I see it like you do: Big Sur also seems to me to run more smoothly and to be faster. Apple has apparently done a lot right at one point.

      • Dirk says:

        Right! They did a lot of work on the performance. No wonder the M1 MacBooks get such good reviews. A lot seems to have to do with the system itself.

        PS: The tip even comes (in a slightly modified form) from the Copy Cloner manual under the heading "What if the Mac does not boot". In this case, you should install the system via restore and then specify your backup hard drive in the migration assistant. In my case, I wanted an up-to-date copy anyway, so I took the original right away, which then happened very quickly, since both are on the same SSD.

        In addition, it is not possible (and it will probably stay that way) to move the system to such an AFPS partition (instead of an external SSD) via Copy Cloner etc., as Apple deliberately prevents this. As far as the bootable backups are concerned, however, it is obviously currently a bug.

  3. toniB says:

    Hi Jens,

    I have just installed BigSur in parallel with APFS!
    Has restarted x times but everything is going perfectly
    (MacBook Pro 15 ″ Late 2013 :-)

    I hesitated at first because I thought that a new operating system would use up more resources and thus slow down my old Macbook.

    In the first tests, I am positively surprised, because it works at least as quickly, if not even faster.

    After getting used to it, I will delete the old system and free up more memory.

    • Jen Kleinholz says:

      Hello Toni! Great, I'm glad it worked out for you. I think you get used to the look of Big Sur very quickly. I can't understand the whining of all the people. The new macOS is really successful ...: D

  4. peleffm says:

    Hello in the round

    Catalina runs on my new Intel Mini 2018 and I print duplex with the AcuLaser C3900DN. EPSON had donated a firmware update again.
    Under Big Sur, printer support is unfortunately no longer provided according to EPSON support.

    Now I take up this post:
    a) Clone of the Catalina set up externally via CCC.
    b) Update Catalina on Big Sur, so do not reinstall it, also to have mail with all mailboxes available.
    c) Reload the clone on the volume via FDP, but then I would have to delete the mail there.
    d) Boot then with the option key to print under Catalina. There is probably. an easier way?

    I hope I got it across in an understandable way
    Thanks for your opinion

    • Jen Kleinholz says:

      Hello Pele! In principle, that's the way to go, although with APFS you could also have two volumes on one hard drive. That saves a bit of "hazzle". But a different approach: Have you tried whether you can use the printer under Big Sur with the Gutenberg driver get up and running? It's not officially updated for Big Sur yet, but it might work ...

  5. Good day. I installed Big Sur, but then discovered that the mObject app for Final Cut Pro no longer works (incompatible). A very expensive app, by the way. I work a lot with this 3D. What do you do now? This is why I raised Catalina again. Now it's working again. But otherwise Big Sur has been doing very well on my MacBook Pro so far. Sincerely, Heinz from Berlin

    • Jen Kleinholz says:

      Hello Heinz! Unfortunately, you can only write to the developer of mObject whether he or she would like to update the app. If nothing happens in this regard, you unfortunately have to stay on the old system or look for an alternative to the app - which probably doesn't exist.

  6. peleffm says:

    Hello, Jens!
    Thanks - I'll be happy to try the driver.

    After reading some forum posts regarding the update on Big Sur, I am convinced that I should forego the update, continue working with Catalina and thus continue to use the printer. At least as long as there are spare parts and toner. I would like to use a € 500,00 printer for as long as possible ...

  7. Ellec 2021 says:

    I have had an iMac 24 for a few days (16 GB RAM, 1TG SSD).
    Big Sur is installed, of course. Now I have tried to install Big Sure on a second volume (created with the hard disk utility). Unfortunately that doesn't work. When I specify the new volume as the target during the installation process, I get the error message: The installation cannot be installed on this computer. What am I doing wrong?

    • Jen Kleinholz says:

      Hello Ellec! Good question ... did you format the volume to APFS? Alternatively, you could try connecting an external hard drive and trying to install macOS on it. Normally, however, it should actually work out as you intended.

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