With that version of Mac OS X, and all versions since, its been possible to use the Terminal command createinstallmedia to create a bootable installer of the macOS, in this article well show you how.
Once you have those two things the process shouldnt take very long.
Youll also benefit from USB 3, or USB Type C - this may be your only choice if you have a newer Mac.
Below well look at how to get Catalina installers as well as how to get older versions of the macOS or even Mac OS X.
New Disk Download Old Mac
We do have a dedicated article about How to download old Mac OS X and macOS versions.
We have included the createinstallmedia code youll need for installing the Big Sur beta via a USB below.
This is because when High Sierra launched Apple stopped making older versions of the OS available to download via the Mac App Store.
If you have already installed this version of macOS, you will see a message warning that the version of macOS is already installed on this computer.
Click on Continue to confirm that you still want to download the full installer.
This process may take some time depending on the speed of your connection and whether you are using a wireless network.
The createinstallmedia command makes it possible to create a bootable copy of an installer on any drive thats connected to your Mac.
Note you wont see characters appear as you type it in, thats fine.
The process can take a while, youll see Erasing Disk: 0 10 20 30100.
Copying installer files to disk Copy complete and so on will appear in the Terminal window.
Plug the external drive into the Mac that you want to install the macOS on.
The process is different to the one described above though, and we cover it here: Read about How to run macOS on an external hard drive here.
Check in Disk Utilities, its the name of the external disk you are using.