Windows cant be installed on VirtualBox, CompareExchange128 Processor Incompatibility

Few days, we posted about an error we just received while installing Windows 8.1 Preview on VirtualBox. As we all know, VirtualBox is the safest way to try out preview versions, because it supplies all the necessary requirements to the Windows edition to tested. Today, we came around another issue while installing Windows 8.1 on VirtualBox. This time, we received an error window: Your PC doesn’t support CompareExchange128. Here is the screenshot:


It appears that this is a compatibility issue, strictly related to virtualization since Windows 8 is running on the same PC. However, VirtualBox parameters must be satisfied when you decide to install any operating system, in addition to normal requirements specified for it. VirtualBox has a solution for this.

The fix is mentioned below, but make sure that you perform it when VirtualBox is not running on your system..

Can’t install Windows because processor doesn’t support CompareExchange128

1. Open Command Prompt with administrative privileges.

2. Type these commands one by one followed by Enter key:

cd "C:\Program Files\Oracle\VirtualBox"

VBoxManage setextradata [vmname] VBoxInternal/CPUM/CMPXCHG16B 1


If you receive the invalid batch command error in executing the last command then try it withcurrent user (non-administrative Command Prompt). Now reboot and try to install Windows 8.1 using virtualization and this time you won’t receive the error.

This article applies to 32-bit preview of Windows 8.1, if you’re going to install 64-bit version of Windows 8.1, then your processor must support CMPXCHG16b, PrefetchW and LAHF/SAHF.

Hope you find the fix helpful!

Check this post if you receive Your Windows install couldn’t be completed error message.

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An Electrical Engineer by profession, Kapil is a Microsoft MVP and a Microsoft Content Creator. Please read the entire post & the comments first & create a system restore point before making any changes to your system.