With its new colorful appearance, macOS Big Sur catches your eye. Except that you don’t want to compromise the stability of your machine. On the contrary, you would like to anticipate future instabilities and incompatibilities, by testing the applications that you need. How to test macOS Big Sur without giving up macOS Catalina? Follow the guide !
Usage warnings
We won’t blame you for wanting to install a beta version of macOS, especially when it contains so many new visuals. But we continue to advise against installing it at any cost, by entrusting identifiers to more or less dubious sites, to obtain the precious configuration profile. If you are not a developer, we recommend that you wait a few days for the first public beta.
As it stands, you may not be able to install macOS Big Sur. Apple explains:
- that you must first install macOS High Sierra 10.13.6 or newer, before installing macOS Big Sur 11.0b1, on the iMac Pro 2017;
- that you may not be able to install macOS Big Sur on external volumes;
- that you will not be able to install macOS Big Sur on a Fusion Drive volume when FileVault is activated.
Finally, if the same APFS container contains an installation of macOS Big Sur and an installation of an earlier version of macOS, you will no longer be able to install updates on this old version of macOS. The coexistence of two systems is never easy, and can turn into a nightmare if the internal program is updated. Never proceed – never – without backup.
Share internal drive
First possibility, your disk is large enough to be shared, and you want to install macOS Big Sur alongside macOS Catalina. Or rather, you think that your disk is sufficiently spacious, which will not necessarily be the opinion of the system. Open Disk Utility, which you will find in the / Applications / Utilities folder, select the disk Macintosh HD, and click on the button Partition.
Disk Utility will remind you that with the APFS file system, you can create a new volume in the existing container, rather than modifying the partition table. Click on Partition. The system partition is completely scratched, and you cannot click the button + ? Even if the Finder assured you there were hundreds of gigabytes left, the disk is full.
You could free up space more or less easily with this or that utility, but nothing is as effective as launching … the Boot Camp Assistant. It may sound silly, but on first launch, it cleans up Time Machine snapshots and cached iCloud files so you can carve a partition. Launch it, let it clean up the files, then quit it and go back to Disk Utility.
You can now click on the button + to create a new partition. Name it and give it a sufficient size, a good hundred gigabytes if you plan to install some professional applications. Click on Apply, then confirm by clicking on Partition and Carry on. The operation lasts a few minutes to a few hours, during which you cannot use your machine.
After partitioning, you can install the configuration profile, from the developer portal (private beta) or the “Apple beta software program” page (public beta). You can then download the macOS Big Sur installer from the section Software update System Preferences. Simply choose your new partition to install macOS Big Sur alongside macOS Catalina.
Use an external drive
Second possibility, your disk is too small, or you want to maintain a sanitary cord between the stable version and the development version. So you want to install the beta on an external drive, a comparatively simpler manipulation, as long as the drive is formatted in Mac OS Extended Journaled format.
We recommend using an SSD rather than a hard drive, favoring NVMe models with a USB 3 interface (Crucial X8, SanDisk Extreme Pro, Samsung T7…) See Thunderbolt 3 (Samsung X5). These disks will provide speeds greater than one gigabyte per second, for perfectly smooth use, even with the most complex applications.
Get started on macOS Big Sur
Whether you have installed macOS Big Sur on the internal disk or on an external disk, go to the section Boot disk System Preferences to choose the system on which your Mac will automatically start by default. Hold the button ⌥ at startup to select the other system on an ad hoc basis.
If you are starting on macOS Catalina, don’t worry about the error message about a “Incompatible disc”. This is one of the small side effects of the coexistence of the two systems, macOS Catalina not including the new APFS functions integrated into macOS Big Sur. This message has no effect on the operation of the two partitions.
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