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


  1. 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. 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. 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. 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. 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. 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. 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.

  10. 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

  11. 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?

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

  13. 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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