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. Opens 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

It is not only possible with APFS to install two operating systems in parallel on a hard drive on an Apple Mac. That was already possible before. However, a so-called “partition” had to be defined for this. That was depending on the procedure (Portcommand, tools with a clear user interface, etc.) sometimes complicated, sometimes simpler. But those times are over with APFS – so 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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79 Responses to “Install macOS Catalina without a partition alongside Mojave”

  1. 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?

    1. 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.

      1. 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?

        1. 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!

        2. 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.

          1. Yes, that's how you pulled everything over. The new Catalina becomes a little cleaner if you only accept selected things with the migration assistant. And even better is a “clean install” where you set everything up again afterwards. It's work, but you should do it every few major macOS updates.

  2. Walter K Siebert

    read done. Now I have two additional “disks” Catalina and Catalina – data. Will it stay that way, or can the two “hard drives” be combined into one “hard drive”?

    1. 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. 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. I read this after I've already "partitioned" the HD. But the result is exactly the same. I also don't see any major difference between what used to be called "partitioning" and now obviously called "creating a new volume".
    Can you give me a hand there?

    1. Yes, that's also what the article says: An APFS volume only takes up as much space from the hard disk as it actually occupies. It kind of "grows" as you use it, 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 only put 500 MB of data on a 2 GB partition, the 500 GB are "gone". So you have to snap off the 500 GB from your main partition.

      1. One more thing: when you click on “Partition” a dialog comes up where you have the choice between “Partition” and “Add Volume”. I'm no longer sure what I chose.
        Is there a way to determine this afterwards?
        My two “Volumes”, “Catalina” and “Catalina – Data” are in the same container.

        1. Yes, if you have Catalina and Catalina data, it's one and two volumes respectively. A partition has only one extra container and none with “data” as a suffix.

  5. 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. 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. 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. 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?

    1. 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.

    2. 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.

      1. 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?

        1. 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.

        2. 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.

          1. 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.

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

          1. 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. 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 to my contribution. Unfortunately I skipped the migration. Maybe that was a mistake, maybe not. Anyway, this has resulted in me now having two hard drive icons on my desktop. Both disks have the known folder structures. So with the new system I can also start or open my programs and data on my “old” hard drive. So far, despite the lack of migration, things are looking pretty good. However, Catalina is only up 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?

    1. 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.

  10. In reply to Martin on November 9, 2019 at 09:45 am (why isn't there a 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.

    1. 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.

  11. 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.

    1. 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.

  12. 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 start volume when the “alt” key is pressed when the MacBook is started, and it is also not available as a start 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???

    1. 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

      1. 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?

  13. Great article! Now I'm wondering if 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 which is only supported up to Sierra. However, “IphoneXR” requires at least High Sierra to import images in HEIC format) I've been looking for a solution all weekend! =(

    1. Hello Calvin! Yes, this should also work with older Mac systems. A partition with a bootable system always appears in the startup manager if you hold down the ALT key during restart.

  14. 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!

    1. 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.

      1. 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!

        1. Hello Fra! So Parallels goes. This is here 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.

    1. 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.

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

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

  17. Ernst Wunderli

    Very interesting and valuable contributions here at Apfelot.
    I'm going to make a Mojave clone on a new external HD and format it with APFS so I can still use 32-bit only software. The most important thing is the expensive Adobe Acrobat Pro and Premiere Elements 2018 that I was able to buy. What 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'm re-entering the installation password. —The main purpose of this scenario for me is that I can still “save” Adobe and keep using it to edit images and edit PDF.

    1. Jen Kleinholz

      Hello Ernst! Currently, it is definitely the case that Adobe recognizes the “pro Mac”. When I clone my hard drive and boot from the external clone I have no problems. That should work for you too. It shouldn't matter whether you reinstall it on an external hard drive or clone it. I hope so... but I would appreciate if you could give feedback on whether it worked.

  18. Hello I have a Mac Pro 5.1 that runs on High Sierra 10.13.6 and an MBP that runs on 10.6.8. I actually wanted to avoid downgrading the Mac Pro, but unfortunately 1-2 programs only work on 10.6.8 and the Macbook won't last too long ...

    Is it possible to create a new volume on the Mac Pro as described here and copy the MBP hard drive with 10.6.8 to it, and then run it on the Mac Pro 5.1 10.6.8 or 10.13.6? Or would 10.6.8 have to be freshly installed on the new volume?

    Thank you!

    1. Hello Benjamin! So in an emergency you can start with a copied system from another Mac model, but that should only be used in an emergency, as the system is actually optimized for a different model and many things should not run optimally.

      So I would recommend reinstalling the 10.6.8 so that it also works with the Mac Pro.

  19. Hi Jens,
    I stumbled upon this article by chance and was thrilled with your great report. My Mac mini is currently running Big Sur 11.6 and the software update notice has long wanted me to decide to update to Monterey. So today I tried to create an installer for Monterey and then move the installation into an image especially for Monterey so that I can install Monterey and Big Sur in parallel and run them separately. Unfortunately the installer keeps breaking off and countless error codes are listed. So is there a different approach for Monterey? In any case, I really like the way you describe being able to create and save an installer file myself. Only then should the installation go through. If you have any helpful tips, I would be very grateful.
    Greetings Andi and all the best for the new year;)

    1. Hello Andi! just look here at Apple itself after. I haven't created an installer for Monterey myself, but I've followed the Apple instructions for the others. You can also use the app ANYmacOS try it out ... it loads the files for you and creates a boot medium from them. But it threw me a lot of mistakes. I think you have to give the app a lot of permissions to make it work. : D

  20. Hi Jens,
    Thanks again for your prompt answer. In the meantime I was able to start the installation process again and without having changed anything, Monterey was successfully installed on the boot volume you created as you described. So the way you described for Catalina and Mojave also works perfectly with Big Sur and Monterey. What surprised me a bit, however, is that a blank operating system is installed. So without presettings or previously installed programs etc.. But actually it's also quite logical. So now I use it to play around with Monterey a bit and to install one or the other program that is important to me and to see if there are any problems. Of course, it would be helpful if there were another option regarding a system update and conflicts with installed programs. So far, such a system update has always been something of a roulette game with unexpected effects. Or am I making a mistake there?
    In any case, best wishes from me and thanks again for showing me the way.

    1. Hello Andi! The second operating system runs completely independently. In fact, there are neither your other users nor the programs installed on the other system. The smaller updates of macOS usually don't cause any problems, but with the larger ones I would always create a bootable backup beforehand. There is no better "insurance". :D

  21. Hi Jens,
    could it be that the 2nd operating system on the Mac Mini is creating a second login for Apple ID and I am thus creating confusion in the contacts?
    I'm not exactly sure what happened yet, but in terms of messaging, face-time, etc., there's a bit of a mess going on now.
    Greetings Andi

    1. Hello Andi! Yes, you also log in there with your Apple ID. But this is basically like signing in to two Macs with the same Apple ID. It doesn't lead to chaos. What exactly do you mean by chaos??? Maybe we have different ideas.

      1. Hello Jens, it took a while, but now I got around to it: If I was logged in to the Apple ID with Monterey and then switch back to Big Sur, I get a message that logging in to the Apple ID failed. If I then log in again, it works again. But the hint made me a bit suspicious. Another shortcoming of this additional star volume: the backup via Time Machine no longer runs because far too much space is now required. Everything can be solved somehow, but if I just want additional security in case of an emergency, I would probably prefer a bootable version of a functioning Mac variant, for example as a USB stick. – It's great that I can of course try out which software I need to run on Monterey first. I think I can finally risk updating my Big Sur system to Monterey. How do you actually remove the extra startup volume when you no longer need it? Sorry if this is going a bit far, but maybe it will help others too. Greetings Andi

        1. Hello Andi! Yes, I think there seems to be some confusion when switching between two systems with the same Apple ID. 😂 If you have two separate Macs with two systems, this is not the case, but apparently it is with a Mac with two systems.
          Regarding your question: I think you could delete the one volume in Disk Utility (make sure you select the right one!). Personally, though, I always do it by copying the system I want to keep to an external disk (with CCC) and then erasing the internal disk. But here, too, you have to make sure that your backup actually works, otherwise you will be left without a system afterwards.
          When trying out new systems, I usually also make a backup of the current one and then the copy of the update to see if everything works.
          That also works with a USB stick, but those things are just as slow as shit. :)

  22. Hello Jens, I have a MacPro (end of 2013) on which I still use High Sierra – so I can still use the old Photoshop CS5. It would be possible to install Big Sur on the computer - I use Big Sur on a MacBookPro from the same year. Now I would like to install the same system on the MacPro for my daily work, since there have been no updates for High Sierra for a long time.
    1. Question Is it also possible in this constellation to “simply” install a second, up-to-date OsX for Monterey as you described?
    2. Do data and programs also have to be migrated, or does Monterey access the existing structure?
    I am looking forward to your answer.
    All the best

    1. Hello Stefan! Yes, in principle you can install a second system, but unfortunately Monterey cannot access the apps installed there. Unfortunately, this is not technically possible.
      I'm sorry I don't have better news.

  23. Hello! I have to come out as an absolute layman right away.
    My question: Can I have a new operating system at the same time as Sierra 10.12.16 (because of the old Adobe Suite)? Does that then run over a “normal” partition?
    Thank you in advance!!

    1. Hello John! Exactly, with the older systems you do this with partitions or with two different hard drives. The only problem is that you can only boot one system at a time. If you work with Parallels Desktop and install an old macOS in Parallels, then both versions can run simultaneously and you can drag and drop files between the systems and even share the clipboard. It costs money, but if you're making money out of the Mac, maybe it's an expense that's worth it because it saves a lot of time and pain.

      1. Thank you Jens for your reply! How exactly do I use a second disk as a system disk? Or how do I copy my operating system or clone everything to the external FP? Is there a guide for this?
        Please excuse the stupid questions and thank you very much for your answer!
        And I'm still thinking about Parallels Desktop...
        Many greetings, Joh

  24. Really great instructions - with all the imprecise instructions on the net, yours stands out so extremely.
    Thank you!

  25. Hello! - The day before yesterday I put a brand new 2018 macmini into operation - but had to set it up again because the @ sign didn't work, tried 3 different keyboards - now I wanted to install Mojave (to use 32bit programs) on an added volume from the AFPS Macintosh HD volume proceeded as described above in the article - only when I click on the icon of the installed installation stick (over 6GB in size), the icon in the dock just bounces up and down. Then tried to boot up via cmd + R and Mojave from the stick but there was a message that for security reasons it couldn't be started from an external medium. I bought the stick from Amazon - unfortunately I don't know what to do anymore. LG Michael

    1. Hi Michael! Your Mac probably has Startup Security set up so that the Mac is not allowed to boot from external media. You can change that yourself in this program. You can find the information about it here in the post.

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