How to run two versions of macOS simultaneously on a Mac using dual-booting.

You can choose to update your Mac to the newest version of macOS or run a beta version without committing to only one. By installing two different operating systems, you can dual-boot your Mac and have access to both versions of macOS. This allows you to select the version that best fits your needs on a daily basis.

In this article, we will discuss the steps for setting up a dual-boot system on your Mac, allowing you to run two different versions of macOS. Before we delve into the process, it may be helpful to understand the advantages of this setup.

Why dual-boot macOS

There are several potential motivations for dual-booting, or running two different versions of the Mac operating system simultaneously.

• If you wish to upgrade your Mac’s software to the most recent version, but have old applications that may not be compatible, establishing a dual boot may be a viable option for utilizing those apps.

• If you are a programmer and require to evaluate your own applications on various macOS versions (especially if it is a frequent task).

• If you would like to test a beta version of the Mac operating system without fully committing to it and potentially causing issues with your apps and data.

One potential source of confusion with dual booting is the process of partitioning. In previous versions of Mac OS X and macOS, users had to partition their Mac. However, newer versions of the operating system allow for the creation of a volume instead. For the purposes of this discussion, we will assume that you are using a more recent version of macOS and will therefore focus on creating a second volume. However, we will also provide instructions on how to create a partition if needed.

Before you start…

Prior to beginning, it is important to note the following information, regardless of which version of macOS you are using:

• Create some room: In order to have the ability to use two versions of the OS on your Mac, you will need to free up space. Learn how to free up space on a Mac. Before beginning, start by removing unnecessary apps (here’s a guide on how to uninstall apps), deleting any unnecessary files and folders, transferring your large photo library to an external drive, and considering what can be deleted from the Other, system, cache, and other categories.

• Reworded: The following crucial step is to create a backup. It is highly recommended to ensure that you have a backup of your Mac before proceeding with any similar tasks, in case something goes awry. We provide instructions on how to back up your Mac here. Additionally, we have a guide on using Time Machine, which is Apple’s software for creating backups.

• Make sure to back up your Mac before partitioning it, as older versions of macOS will require a complete wipe. If you want to preserve your current work, make sure it fits on the smaller partitioned drive. Fortunately, no wiping is necessary if you are only creating a volume.

• There are other options available. If erasing your Mac seems like too much effort, you can consider installing a different version of macOS on an external hard drive. We provide instructions on how to do this in our guide: “How to use an external hard drive to run macOS.”

• Ensure that your Mac can support the desired versions of macOS: It will not be possible to run a version of macOS on a Mac that does not have the necessary compatibility. Determine the macOS version that your Mac is able to run.

Instructions for increasing the volume on your Mac computer.

To have two macOS operating systems on your Mac, the approach will vary depending on your current macOS version. If you have High Sierra on an SSD or any version from macOS Big Sur onwards, the process is simpler as your Mac uses the Apple File System APFS.

The previous file system, HFS+, has been replaced by APFS. APFS offers several benefits, with one significant advantage being Space Sharing. This feature allows for the sharing of available space among different volumes on the disk, meaning that more space can be allocated at any given time instead of being designated to a specific volume during its creation, as is typical for partitioning.

If you are currently using APFS, you have the option to generate an APFS volume, which we will demonstrate below. From there, you can simply install the updated version of the operating system on that volume without having to reformat any data. This process is incredibly straightforward.

Using an outdated version of macOS or Mac OS X can make the process more convoluted.

Ways to generate an APFS partition.

1. Make a backup of your Mac (as it is always prudent to do so before embarking on an adventure).

2. Launch Disk Utility (located in the Utilities folder within Applications, or use Command + Space to search for it).

3. Select the option next to the View button on the toolbar and opt for Show All Devices. This will ensure that you have visibility of all the volumes in your disk. Most likely, you will have a volume labeled Home or Macintosh HD.

4. Choose the Home volume (or Untitled) and press the + symbol to generate a fresh volume. For additional assistance, we suggest referring to our comprehensive instructions on this procedure: How to divide a Mac hard drive or SSD, or establish an APFS volume.

5. To properly name your volume, consider using “Beta” if you are installing the beta version.

6. You have the option to set a storage limit, but it is not required. To establish a size restriction, go to Size Options and enter values for Reserve (minimum) and Quota (maximum). Historically, we have set the limit at 25GB. While this number can be adjusted, it is a complex procedure and we recommend against implementing a limit.

7. Next, select the “Add” option to include your new Volume to the Mac.

After successfully setting up your second volume, you can proceed to installing the beta version of macOS or a different version from what you typically use. We will discuss the steps for doing so in the following section.

If your Mac operating system is not up-to-date and does not have APFS, the process will be slightly more complicated as it requires creating a partition.

How to set up two different versions of macOS on a Mac computer.

After successfully following the instructions provided, you can proceed with installing the next version of macOS on your device.

1. Obtain the installation file for your desired operating system. You can acquire it through Software Update or the Mac App Store (refer to “How to update macOS” for instructions on obtaining the installer). Please note that the version you download must be newer than your current one – otherwise, the installation process will be more complex. If this is the case, refer to “How to downgrade to an older version of macOS” for guidance. Download the file, but do not initiate the installation process yet.

2. Install the alternative macOS on the new volume you created instead of your main volume by selecting it during the installation process.

3. Please be patient as your Mac installs the updated operating system on the new volume.

4. After the process is complete, your Mac will boot from the volume containing the newly installed operating system.

5. To return to your previous version of the operating system, simply power off your Mac and hold down the Alt/Option key while it restarts. This will give you the option to open from your original volume and select which version of macOS you want to use.

6. Upon starting your Mac, you may be prompted to select a network and enter a password. However, we have found that this step can be skipped.

Steps for setting up the beta version of macOS on a different partition.

The procedure is the same if you wish to install a beta version of macOS on a different volume.

To begin, if this is your first time, you will need to register for the beta and get the macOS beta software. When it has finished downloading, you must install it on the newly created volume following the given instructions.

We have a detailed explanation of how to sign up for the macOS beta and How to get the macOS beta.

We also offer guidance on how to download previous versions of macOS. For operating system options other than macOS, you may find our tutorials on how to install Windows or Linux on a Mac helpful.

How to add a second macOS to a Partition.

Before creating a partition, you must wipe your Mac. As mentioned previously, it is important to make a backup before proceeding.

The easiest method for creating a partition is as follows:

1. To enter Recovery mode on macOS, power on your Mac and press and hold the Command and R keys until the Apple logo or spinning globe appears.

2. After entering Recovery mode, utilize Disk Utility to erase the primary hard drive and divide it into two separate partitions.

3. Retrieve your Time Machine backup onto the designated partition. Keep in mind that you cannot retrieve a backup from a newer macOS version than the one you intend to use on this partition.

4. Another option is to use the Install feature in Recovery to install the desired version of macOS onto the primary partition.

5. Next, it is necessary to install an alternative version of macOS on partition 2. Refer to the instructions here for installing a second macOS version or the beta for the upcoming macOS version on the second partition.

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