Upgrading from Windows Enterprise 8 to 8.1 on Oracle VirtualBox Using OS X

I’ve been using Windows 8 Enterprise with Oracle VirtualBox on my MacBook Pro, which runs OS X Mavericks (10.9).  Now that Windows 8.1 has been released, I decided to upgrade.  I had read that the upgrade was fairly easy, and could be done through the Windows Store.  This is not always the case – such as when you are running the Enterprise version.

If you are running the Enterprise version of Windows 8, you must install from DVD media, or a mounted .iso, or equivalent.  I downloaded the iso file from MSDN and mounted it in OS X to install the upgrade.  At this time, I came across an error I had never seen before:

“You can’t install Windows 8.1 because your processor doesn’t support CompareExchange128″.

Fortunately, this can be easily fixed.  Open a Terminal Window and change directories to your VirtualBox.app directory.  (This step may be unnecessary if your path is set up correctly.)

Next, at the command prompt, type:

vboxmanage setextradata [vmname] VBoxInternal/CPUM/CMPXCHG16B 1 <ENTER>

“[vmname]” should be the name of your VM, which in my case was “Windows 8 Enterprise”.  Quotes are necessary if there are spaces in the name.

Restart your Windows 8 VM and try to install again!

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