Change Your Thinking About OSes

Virtual machines (VMs) have a number of features and properties that require a new way of thinking about operating systems (OSes) so that you can take full advantage of a VM.

Doing a major OS update on your Mac®—or even installing a macOS® from scratch—scares many users.

“What if the update fails, will my Mac even boot afterwards?”

“What if an app I need will no longer work after the update?”

These are valid concerns about your host OS—the OS that boots when you turn on your Mac. There are even whole books written about how to do a particular macOS upgrade:

OSes  OSes OSes OSes 


However, OSes installed in a VM are different. Changing the way you think about OS upgrades or installations—or even day-to-day use of an OS—is needed to take full advantage of a VM. Here are some features of VMs or scenarios that require this change:

Rollback Mode (also called “Undo Drives”)

I think Rollback Mode is one of the most powerful, but least-used features in Parallels Desktop® for Mac. Enable Rollback Mode (Figure 1), boot the VM, then do anything you want in that VM: delete or add files; install, update, or delete an application; install an OS update; change some setting, and more.


When you shut down the VM, you will get the option to discard any changes you made, or to keep the changes (Figure 2). If you choose discard, it’s like a giant undo. Everything you’ve done since you booted the VM is gone—no matter what you did.


In my experience in talking with Parallels Desktop users, they accept that you can roll back the addition of a file, but they find it hard to believe you can roll back the deletion of a file. So I made a little video to show you Rollback Mode in operation. (See Video 1.)

Test a Beta OS

Both Apple® and Microsoft (as well as some others) provide public beta versions of their forthcoming OSes so that interested users can test them, experience new features, and report back when issues are found.

Only very brave (or very foolhardy) users install a beta OS on their main computer. By their very nature, beta OS versions have bugs and half-finished features. These can cause you significant problems, including—in extreme cases—the loss of all your data.

If you happen to have a spare Mac or PC that isn’t being used, you can install these beta OSes on the spare, and you don’t risk significant data loss. Most people don’t have a spare computer laying around. However, you can usually install these beta OSes in a virtual machine. I have been doing this for years, both with beta macOS and beta Windows releases. In doing so, you risk very little, if anything.

In Figure 3, you can see beta releases of both Windows and macOS being used in VMs—with no risk at all to my Mac.


Figure 3_Win10 beta and High Sierra beta in VMs

Test an OS Update or Upgrade

As mentioned in the beginning of this post, an OS update or upgrade can be a scary experience for many users. These fears are not unfounded. Just read one of these:

How to fix a Mac that won’t finish a macOS update

MacBook will not start after macOS Sierra update

Boot failure after High Sierra update

Windows update borks elderly printers in typical Patch Tuesday style

I don’t know of a completely foolproof way to prevent these, but if there are reports of problems with a particular update or upgrade, I first test it out in a VM. You certainly could use Rollback Mode for this, but for a major update, I usually do this:

  1. Make a clone of the VM (Figure 4). This makes a complete duplicate of the VM. If your VM is large, you will need sufficient space on your Mac for the clone.

Figure 4_Creating a clone of a VM in Parallels Desktop

  1. Apply the update or upgrade on the clone.
  2. If you experience problems with the update, or problems when using the clone, throw the clone away. Wait for the problems to be addressed before trying again.
  3. If you have no problems after a few days, then throw the original VM away and keep the clone.

I hope this new way of thinking about OSes enables you to take full advantage of the power of VMs in Parallels Desktop. If you have any other interesting ways to use VMs, let us know in the comments.

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