The introduction of macOS Mojave brought a wealth of new features, but for one particular Mac, it also lost one. If you have a late-2012 27-inch iMac with a 3TB hard drive, you can’t upgrade to the new operating system if you have Boot Camp configured. Before you can proceed, you have to back up your data and use Boot Camp Assistant to delete your Boot Camp partition.
So what is Boot Camp? Ever since Apple switched to using Intel processors for Macs in 2006, it’s been possible to install an operating system designed for the PC on a Mac too. This means it can run (for example) Windows or Linux instead of macOS. Boot Camp lets you partition your hard drive and install macOS on one partition and an alternative operating system on the other.
You have to shut down your Mac and reboot when you want to switch from one operating system to the other, but it’s still very useful if (again, for example) you love macOS but you need to use software that’s Windows-only.
But there’s another way, and this time, it works even on the affected iMac that can’t use Boot Camp with Mojave. It’s called virtualisation.
Virtualisation is, in a nutshell, running a virtual computer that’s hosted by your main operating system. This is called a virtual machine. With Virtualisation, you no longer need to partition your hard drive, and you don’t need to reboot to switch from macOS to your other operating system.
You can open a Windows or Linux virtual machine from within macOS without rebooting. You can copy and paste files and data between your virtual machine and your Mac’s apps, and run a Windows or Linux application from within macOS, with its host operating system running invisibly. You can even run older versions of macOS alongside your current release.
The fact that the Boot Camp problem only affects one particular model of Mac suggests the incompatibility was an oversight rather than deliberate policy on Apple’s part; it seems unlikely the rest of the Mac range will drop Boot Camp any time soon, and maybe the affected iMac will get an update to bring the feature back.
Even so, if you regularly use Windows, Linux or any other operating system on your Mac, virtualisation is a superior option. Both Parallels Desktop and VMware Fusion offer a free trial period, so you’ve nothing to lose by giving them a go.