Processor doesn’t support CompareExchange128, Can’t install Windows

Few days, we posted about an error we just received while installing Windows 10/8.1 on VirtualBox. As we all know, VirtualBox is the safest way to try out preview versions, because it supplies all the necessary requirements for the Windows edition to tested. Today, we came around another issue while installing Windows 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 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.

If you receive error You can’t install Windows because your processor doesn’t support CompareExchange128 while installing Windows 10/8.1 using virtualization on VirtualBox, read on.

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 and hit the 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 with current 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 a 32-bit preview of Windows; if you’re going to install the 64-bit version of Windows, 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.

Posted by on , in Category Windows with Tags
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.


  1. JoJo

    What is this for bullshit, I have an old pc that I have recently reinstalled with Windows 8 with no problems.
    Now I wish to install windows 8.1 RTM and I run in to this error.

    What is so different about windows 8.1 compared to Windows 8 that they decided that your processor needs to have this CompareExchange128.. what the hell does it even do?

  2. ^^ Modern processors are built with CompareExchange128 capability so that doesn’t makes too much differences. This also shows that how Windows 8.1 is different than Windows 8 🙂

  3. amigabill

    I had to do this to upgrade from 8.0 Pro 64bit to 8.1 Pro 64bit Release (not Preview) as well. The article makes it sound like I should not have had to do this, as I’m already in 64bit for 8.0 running fine.
    For anyone else trying to upgrade to 8.1, give this a try, even if your
    8.0 is running in 64bit just fine. The MS Store initially gave a very
    vague message that my CPU is not compatible. Some questing found me an
    updater program form MS that gave the more useful error message that my
    CPU does not have CompareExchange128. I did the edit shown in this
    article, and the MS store now lets me download the update to 8.1. Thank

  4. jf46992000

    amigabill, please give us line by line of what you did to install 8.1 Pro 64bit. The above talks about VirtualBox only. I am trying to install it to the HD from windows 8.0 Pro with Media Center.

  5. dbrohm

    Re: how to fix the Compare exchange 128 error on upgrade of vm running 8.0 64 bit to 8.1 64 bit. This post says that for a 64 bit upgrade the command must include CMPXCHG16b, PrefetchW and LAHF/SAHF

    I was not able to figure out how the 32 bit command line shown below should read to include the 64 bit parameters. I would appreciate it is someone could explain or edit the following command line to show me how it should read.

    vboxmanage setextradata “Win8 Eval” VBoxInternal/CPUM/CMPXCHG16B 1

    Thanks in Advance

  6. Sam

    I am using win7 64-bit and wish to upgrade to win8.1 64-bit. But while installing,i get the error mentioned in this article. but i dont have oracle installed in my PC, so, i cant use the command. Can you please guide me on how to fix it?

  7. ^^ Have you installed VirtualBox before? It may possible some VirtualBox traces are still alive on your system. If its true, install VirtualBox again, execute this command and then re-try to install. If that doesn’t makes sense, Windows 8.1 may not work on your system and you should consider upgrading of processor.

    Good luck 🙂

  8. Kailashkar Kai

    hi guys i am going to give the solution for this , those who run win 8 can definitely run 8.1 for sure
    i met the same problem before but i am using 8.1 now and i am giving the solution from 8.1
    i know you gus will be eager , just do one thing thats enough just update your BIOS from yor motherboard and processor vendor for free thats really enough you all guys run LAHF/SAHF after pentium 4 and pentium D but some pentium D has chances. enjoy ireally worked hard to try this

  9. ^^ Thanks for sharing this, will be helpful to others 🙂

  10. Leonardo Monday

    Microsoft should be sued over this… i bought windows 8 and they need to keep support for this system until the time they advertised it … now they want to drop windows 8 support next year, this is ridiculous.

  11. DGCupit

    For Windows 8.1 x64:

    VBoxManage setextradata Windows-8-x64 VBoxInternal/CPUM/CMPXCHG16B 1
    VBoxManage setextradata Windows-8-x64 VBoxInternal/CPUM/PrefetchW 1
    VBoxManage setextradata Windows-8-x64 VBoxInternal/CPUM/LAHF 1
    VBoxManage setextradata Windows-8-x64 VBoxInternal/CPUM/SAHF 1

  12. Jeanem

    I have a Dell optiplex GX620 pentium 4 but i cant install windows 8.1 buy the store or with the CD ? or anyone can help me?


    vboxmanage.exe: error: Could not find a registered machine named ‘[win7to81]’

  14. ndr

    skip the [ ] characters and if you have space between words, example: Win7 to 8.1 then you have to type “Win7 to 8.1”


    i checked with coreinfo, and it clearly states that all 3 sets: CMPXCHG16b, PrefetchW and LAHF/SAHF are supported.

    even then i get compare exchange 128 not supported by processor.

    my board is dg31pr intel original, supplied as LG PC, i feel, LG has deliberately altered BOIS not to support com ex 128,

    what say?

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