VirtualBox CompareExchange128 Error

Today, I attempted to upgrade my Windows 8 machine to the yet-to-be-released Windows 8.1, and I got the following error:

You can't install Windows 8.1 because your processor doesn't support CompareExchange128.

error

I am running 64-bit Mac as my primary operating system, and have set up 64-bit Windows 8 on a VM using VirtualBox.

Cause

One of the additional system requirements for 64-bit Windows 8.1 installation is that the CPU must also support CMPXCHG16b, PrefetchW and LAHF/SAHF. And this setting is disabled in VirtualBox by default.

Please check out this link for the other system requirements for Windows 8.1.

Solution

Open up the command prompt of your choice – Terminal / iTerm, and execute the following command:

VBoxManage setextradata [VM_Name] VBoxInternal/CPUM/CMPXCHG16B 1

And, that’s it! You’re ready to install Windows 8.1!

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2 responses to “VirtualBox CompareExchange128 Error

  1. Jim Mclaughlin October 31, 2013 at 09:43

    I have a very similar situation but am running Win 8 in Vbox within Vista 64 and get the same message when upgrading to Win 8.1. Would same advice apply and where would commands be inserted ? within Vista or within virtual win 8 ?

    • Sanchit Bahal October 31, 2013 at 10:20

      Yes, the same commands would apply. The problem is with VirtualBox, so the commands have to be executed on the host machine, Vista in your case.

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