October 3, 2013
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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.
I am running 64-bit Mac as my primary operating system, and have set up 64-bit Windows 8 on a VM using VirtualBox.
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.
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!