Install macOS Catalina without a partition parallel to Mojave

Install the new macOS Catalina without having to forego Mojave (or High Sierra)? That sounds absurd at first, but it isn't at all. Because you can install both operating systems in parallel on your hard drive on your Apple Mac and use them with their respective advantages (and disadvantages). This is conceivable if you deal professionally with macOS 10.15 Catalina, but not the many Problems and Limitations want to accept. Even if you want to continue to use 32-bit apps under macOS 10.14 Mojave, you can install Catalina in parallel with Mojave without a partition. Here I'll show you how to do it.

Install macOS Catalina parallel to Mojave without a partition? This works out! How, I'll show you in this guide.

Install macOS Catalina parallel to Mojave without a partition? This works out! How, I'll show you in this guide.

The pioneer: APFS file system

The Apple File System (APFS) is responsible for making parallel installation and alternating use of two operating systems on the Mac entirely possible. And in a very simple way. It is no longer necessary to create a new partition and reserve it for the second system. There is also no need to move to a second hard drive or external data carrier. You can find some more information about APFS in this guide. The following is now about the instructions with which you can install macOS Catalina without a partition parallel to Mojave or High Sierra.

Instructions: Use two macOS versions without a partition on one hard drive

Apple makes it really easy for one to accomplish this feat under APFS. Basically, all you have to do is create a new volume (a kind of virtual hard drive) and install Catalina on it. But there are one or two small hurdles. So that you don't trip over it, here are the instructions:

  1. Open Disk Utility (via Launchpad or Spotlight)
  2. Make sure your hard drive is operating in the APFS file system
In order to be able to install two macOS versions without partitions on a hard disk, it must be formatted in the APFS file system.

In order to be able to install two macOS versions without partitions on a hard disk, it must be formatted in the APFS file system.

  1. If this is the case, click on the "+" above the word "Volume"
Adding a new volume to install the other system or Catalina in addition to Mojave or High Sierra can be done here.

Adding a new volume to install the other system or Catalina in addition to Mojave or High Sierra can be done here.

  1. You will now be asked for the name and format of the new volume
  2. You can freely assign the name ("Catalina" is a good idea); you leave APFS as the format

This creates the basis for the double installation of operating systems on your Mac. But when you try to install Catalina next to Mojave, you may not see the new volume. Don't worry, this is normal. This is how you do it:

  1. Start the macOS Catalina installer from your hard drive (that's how you get it)
  2. The note where the OS will be installed now shows the regular hard drive (Macintosh HD)
  3. You select your new "Catalina" volume by clicking on "Show all volumes ..." below
  4. In addition to the Macintosh HD, the hard disk space created with the above steps is now displayed
  5. Select this and complete the installation

Choose a startup disk and switch between Mojave and Catalina

Now you want to determine or at least check which volume the Mac boots from when it starts. To do this, simply open the system settings ( -> System settings ...) and then select the item "Startup volume". In the window that opens, you can now specify which system should be loaded when the Mac starts. 

If you want to change this directly at start-up and use the other system, then stop immediately after switching on the computer Option key (option, old or ⌥) pressed. This will take you to the start volume selection. Unfortunately, you cannot simply switch between the two systems during operation. Here a restart of the computer is necessary before or during which you switch to the other system using the options shown.

Partitions are now unnecessary and are no longer recommended

Not only with APFS is it possible to install two operating systems in parallel on one hard drive on the Apple Mac. That was already possible before. However, a so-called “partition” had to be defined for this. Depending on the procedure (terminal command, tools with a clear user interface, etc.), it was sometimes complicated, sometimes easier. But those days are over with APFS - basically with macOS 10.13 High Sierra. 

Apple itself no longer recommends partitions under the current file system, as described in the support document HT208891 emerges. Partitions, the required size of which is not automatically determined and must be specified by the user, are used for the file system Mac OS Extended recommended. You can find the note at the bottom under the heading "Further information".

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  1. Dirk says:

    Just to understand ... when starting with Catalina you would have to reinstall all programs / data or somehow migrate?
    Or does Catalina use the existing installations / data ... no, that would be too much of a good thing and just a dream - right?

    • Sir Apfelot says:

      Exactly, you have to migrate things like if you installed Catalina on a different partition / hard drive. The advantage of the APFS volume is simply that it only takes up as much space as it uses. With a partition you have to specify how many GB it should have and no matter how much data is in it - this space is always occupied by the partition.

      • Gunnar says:

        Well, then I have a new, clean Catalina startup volume and the old Mojave startup volume on one disk. Does the migration assistant also work in this constellation? Or are there any problems?

        • Sir Apfelot says:

          Hello Gunnar! You have to test that, because I don't have a Catalina installed. I just don't know. But if you could try it out, it would be great if you could reveal the result here. This is certainly also interesting for others who want to downgrade. Thank you!

        • Martin says:

          I think the migration assistant works.
          But you can also simply copy (clone) everything you want to take over from Mojave, for example with Carbon Copy Cloner, including the system, then start up from it and now upgrade to Catalin.
          So you can be sure that nothing falls by the wayside.

          • Sir Apfelot says:

            Yes, that's how you pulled everything over. The new Catalina is a little cleaner if you only take over selected items with the migration assistant. And a "clean install" is even better, in which everything is set up again afterwards. It does work, but you should do it every few major macOS updates.

  2. Walter K. Siebert says:

    Read done. Now I have two additional "hard drives" Catalina and Catalina data. Will it stay that way, or can the two "hard drives" be merged into one "hard drive"?

    • Sir Apfelot says:

      I think it will stay that way. However, I have not yet created such an APFS volume and cannot report from my own experience.

  3. Small says:

    First of all, great instructions. Have you understood and now 2 systems on my MBA. Both are running and so far I can't see any errors on Catalina.

    Second, however, a question: I have now found that I have 2 new APFS volumes, a Catalina and a Catalina data. Is it correct?

    Sincerely, Mic

  4. Martin says:

    I read this after already "partitioning" the HD. But the result is exactly the same. I also don't see any significant difference between what was previously called "partitioning" and is now obviously called "creating a new volume".
    Can you give me a hand there?

    • Sir Apfelot says:

      Yes, that is also stated in the article: An APFS volume only takes up as much space from the hard drive as it actually occupies. It "grows" so to speak with use or shrinks again when you delete some of it. A partition has a predetermined size - no matter how much data is on it. So even if you put only 500 MB of data on a 2 GB partition, the 500 GB are "gone". So you have to squeeze the 500 GB off your main partition.

      • Martin says:

        All right. It's a shame I did it before I read these tips.

      • Martin says:

        One more thing: if you click on "Partition", a dialog appears where you can choose between "Partition" and "Add Volume". I'm not sure what I chose anymore.
        Is there a way to determine this afterwards?
        My two "Volumes", "Catalina" and "Catalina - Data" are in the same container.

        • Sir Apfelot says:

          Yes, if you have Catalina and Catalina data, it's one and two volumes, respectively. With a partition there is only one extra container and none with "data" as a name extension.

  5. Karin with M says:

    Super guide!
    Already wanted to sell my audio interface as it is no longer supported by Catalina. At first I thought of downgrading and then I got the idea of ​​having two operating systems.

    Long story short.

    Thanks for the workaround :)

  6. Nabo says:

    Hi, everything is really well described! Many Thanks! Unfortunately, my problem is a little different. I installed Catalina and realized too late that I still have to be able to use Mojave for certain work.
    Setting up an additional APFS volume is not difficult, but downloading and installing the old system software is….
    Would be very grateful for appropriate tips!

  7. Erich says:

    My problem: My Mac is running Catalina and I want to create a second startup volume with Mojave. Create a volume, download the Mojave Installer, no problem; however, start installer on Mac with Catalina is denied (message Installer out of date). Is there a solution?

  8. Eyrie says:

    I tried your tip and it worked fine, thanks!
    Now of course I have a new user under Catalina and can no longer access my user's files under Mojave. Is there also a solution for this?

    • Sir Apfelot says:

      Maybe you can import your data with the migration assistant. Then everything is under Catalina. But there is no way to use the data in parallel with both systems. Technically, they are separated like two partitions or hard drives.

    • Martin says:

      I'm better off with my solution of cloning first and then updating. My user is the same and I have access to the data on the Mojave volume.

      • Eyrie says:

        I am trying to understand that. You create the new volume, clone the system and user on it (this would not work for me due to lack of space), then boot from the new volume in Mojave and update to Catalina. But then you have your user twice, right? Can you really access the same user with Catalina and Mojave now?

        • Sir Apfelot says:

          Hello Horst! No, it is not possible for both systems to access the same user. You have both systems separated, as with a separate hard drive or an extra partition, only that they dynamically divide the memory through the APFS volume and you do not have a fixed allocation of storage space as with a partition.

        • Martin says:

          In terms of the procedure, that's the way it is. Because of the space, I didn't clone any of my own documents.
          But it is true: I have two users and my only concern is not to have my data duplicated and therefore I also access my folders in the retained Mojave from Catalina.

          • macfan says:

            I cannot access my Mojave user from Catalina because of the rights. How you do that?

          • Martin says:

            Sorry for coming so late with an answer.
            Since I first made a clone of my Mojave system on the Catalina volume and only then updated it to Catalina, I have the identical user there - and this user now also has access to the data on the Mojave volume.

        • Dominic Hansert says:

          After installing Catalina on a 2 partition, can you delete the Mojave partition, is there any recovery data on the Catalina partition?

          • Sir Apfelot says:

            Hello Horst! If you delete Mojave, the recovery partition will not be affected. That would only be gone if you would not delete the partition, but the entire hard drive. In this way: Yes, you can delete Mojave without hesitation. In any case, I would make sure that I still have a backup.

  9. Nabo says:

    this is exactly where I am stranded ...

  10. chris says:

    Hi all,

    First of all, I would like to express my great praise to you, Sir Apfelot. Not just because of this article, but for this excellent website in general. So far, I haven't found such an interesting, well-founded and helpful site on the subject of iOS. I find almost every article interesting and don't just read the introduction.

    Now for my contribution. Unfortunately, I skipped the migration. Maybe it was a mistake, maybe not. In any case, this has led to the fact that I now have two hard drive icons on my desktop. I have the familiar folder structures on both disks. With the new system, I can also start or open my programs and data on my "old" hard drive. So far it looks pretty good despite the lack of migration. However, Catalina only runs for half an hour and I don't know what else I'll come across.

    I was able to determine two disadvantages, certainly due to the lack of migration. On the one hand, I cannot see the programs on the Mojave hard drive in the Lauchpad and, on the other hand, Catalina does not recognize that programs for certain file types exist in Mojave.

    Is there a possibility, besides a new installation of the programs, to migrate them to Catalina afterwards?

    • Sir Apfelot says:

      Hello Chris! Thanks for your great praise. That pleases me very much. : D Regarding the question: If you have two hard disks, both hard disks are also displayed ... this is in principle not an error. If that bothers you and one of the hard drives is external, you can unplug it. Regarding your question about the programs: Yes, you can use the migration assistant (you can find it under Programs> Utilities) to drag them over from your old hard drive or a backup at any time. Then you save all the individual installation processes.

  11. macfan says:

    Reply to Martin from November 9, 2019 at 09:45 am (Why is there no "Reply" button on the post?):
    Many thanks for your response. I would not have thought that the rights would also be transferred in this way. Unfortunately, I can't try this because I don't have enough free space on my SSD to clone the entire Mojave.

    • Martin says:

      The reply button is further up next to my first post. Of course, I didn't clone everything, only the system, program and the user folder, but omitted my personal documents.

  12. Tom says:

    Hello Sir Apfelot,
    I can only agree, kudos for the good and detailed explanation.
    My question is ! I have Mojave OS and would like to try that with High Sierra or Sierra. So pack the old version onto the APFS volume as described. I am having problems with video files that can no longer be opened and played in Mojave. These are mp4 and mov files. Unfortunately I missed converting these files when switching to Mojave.

    • Sir Apfelot says:

      Hello Tom! In principle, you can install any macOS on this volume. It just has to be able to do APFS. That means, from macOS High Sierra (Sierra not yet!) You can use APFS volumes.

  13. Cidero says:

    Hello Sir Apfelot,

    currently have Catalina on it and would like to use Mojave next to it - so the other way around. ????

    Now I have the macOS 10.14.6 thanks to these instructions ( and generated a bootable stick using DiskMaker X (Mojave version).
    BUT unfortunately the stick is not recognized as a startup volume when the "alt" key is pressed when the MacBook is started, nor is it available as a startup volume under system settings. Have already regenerated twice.
    And from 10.15.2 Catalina (Mojave installation app in the applications folder) only an error message comes up.

    Any suggestions???

    • Sir Apfelot says:

      Hello cidero! I just googled this and apparently there are some sticks that are just not recognized as a boot volume. Another user ordered a new stick and it worked with it, although he did everything as before. Otherwise you could just check whether the stick has a GUID partition scheme. LG! Jens

      • Cidero says:

        I was afraid of it.
        Yes, it is GUID.

        And the error message when installing from Catalina is normal, since it is newer than Mojave, right?

        • Sir Apfelot says:

          Yes, I think the error message is normal. That always comes when you want to install an older macOS (at least I think).

  14. Calvin says:

    Great article! Now I am wondering whether this also works with an older operating system. That means it would be possible to partition the hard drive on my MacBookPro and install "Sierra" on one half and a newer system, for example "Mojave", on the other half. (I have an expensive CAD program that is only supported up to Sierra. For the import of images in HEIC format from "IphoneXR", at least High Sierra is required) I have been looking for a solution all weekend! = (

  15. Markus says:

    Hello, I'm Markus and I also tried to run Mojave on an external hard drive with Catalina on a Mac Book Pro from February 2020. But unfortunately that doesn't work and the system stops briefly with the following window: The version of MacOS on the selected hard drive must be reinstalled. I worked on it for days and spent hours on the Apple Care Hotline, but no one really knew about it and just said that it should work. Yesterday an Apple employee informed me that Macs that are already shipped with Catalina cannot be started with an earlier version, not even with an external hard drive or stick solution. Can anyone confirm this, or are there any other options besides a virtual solution? Thank you in advance and thank you for the great solutions in this chat!

    • Sir Apfelot says:

      Hi Markus! The statement from Apple support is unfortunately correct: If the Mac, like the MacBook Pro 16 inch, was already delivered with Catalina, you cannot install an older system on it or boot from it if you have it on an external hard drive. Another reader was told that too.

      • Siebert Walter K. says:

        I can only confirm. That's why I still have an old MacBook.

      • From says:

        Dear Sir Apfelot, does that really mean that your above article will then be obsolete for all Macs that come with Catalina?

        Would Martin's suggestion of cloning the disks (above) still be a way to get older 32-bit apps running?

        Or Parallels ??

        Thank you!

        • Sir Apfelot says:

          Hello Fra! So Parallels goes. This is . described.

          Cloning the Mojave partition is also possible if you have not yet updated to Catalina. Then you would clone Mojave, for example, to an external disk and only update the internal one to Catalina. So you can still run the 32-bit apps on the external one.

          Regarding the question with the Macs: If you order a MacBook from 2018 now, it will also be shipped with Catalina. However, since copies of this model were released with an older macOS in 2018, you can of course also downgrade here. Only if a macOS other than Catalina has NEVER been used on the model, then nothing but Catalina or a higher macOS can be run on this Mac.

          In practice, this means that the 16-inch MacBook Pro and the new Mac Pro do not accept anything other than Catalina or higher.

  16. Markus says:

    Thank you for the prompt answers.

  17. Peter Wieler says:

    Hello, the following question. If I have installed Catalina, can I still install the old system? So the other way around? Thanks, Peter

    • Sir Apfelot says:

      Hi Peter! Since you are creating two separate volumes, you can understand it as if you had two separate startup volumes. You can have a Catalina on one and also install Windows on the other (with Bootcamp) or another macOS or OS X of your choice.

  18. K. Uwe says:

    I also installed mojave and catalina, initially on two partitions, now that I understood the ingenious principle of APFS, installed everything on one disk and did a clean install at the same time. Everything is going well, only one problem arises every time and after a change of systems: iCloud "complains" and checks the password request every time, etc. I also ask myself whether the sync services work correctly with other clouds and manage the switch correctly, also affects Synology Drive, because data loss would not be a nice result if incorrectly synchronized.
    If someone has already gained experience, I would be very happy to receive feedback.

  19. Petra says:

    Hi, I have the same "problem" with the iCloud password request. As an experiment, I logged off my iCloud on Mojave, I'm logged in on Catalina - since then I haven't been asked for my password.

  20. Ernst Wunderli says:

    Very interesting and valuable contributions here at Apfelot.
    I'm going to do a Mojave clone on a new external HD and format it with APFS so that I can still use software that only runs on 32-bit. The most important is the expensive Adobe Acrobat Pro and Premiere Elements 2018 that I could still buy. Do you think I have no problems installing it on a new external HD. It could be that Adobe refuses to do this as a second installation, even though I still re-enter the installation password. —The main purpose of this scenario for me is that I can still "save" Adobe and continue to use it to edit images and edit PDF.

    • Jens Kleinholz says:

      Hello Serious! At the moment it is definitely the case that Adobe recognizes this "pro Mac". If I clone my hard drive and boot from the external clone, I don't have any problems. This is how it should work for you too. It shouldn't matter whether you reinstall it on an external hard drive or clone it. I hope ... but I would be happy if you could give us feedback as to whether it worked out that way.

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