Can I turn a Win8 installation for UEFI into BIOS-CSM-Mode Win8?

Discussion in 'Windows 8 Help and Support' started by pstein, May 31, 2013.

  1. pstein

    pstein Honorable Member

    Mar 20, 2010
    Likes Received:
    On my computer there is a pre-installed Windows 8 which works fine for
    UEFI boot (Secure boot not necessary).

    Now when I switch in UEFI setup at boot time the UEFI mode into the CSM (BIOS) mode
    and restart then Windows 8 is not starting any more.

    As far as I find out an UEFI-based Windows 8 can only boot with UEFI mode enabled.

    So my question is: Can I turn an existing UEFI based Windows 8 installation into
    an CSM/BIOS based installation (=a Win8 which boots successfully even when I enable CSM in UEFI setup) ?

    If yes: How do I do that?

  2. Saltgrass

    Saltgrass Excellent Member
    Microsoft Community Contributor

    Oct 16, 2009
    Likes Received:
    The CSM (Compatibility Support module) is part of the UEFI enabled boot. It is used to set the system to full secure boot, or allow for other types of UEFI installs. The other bios mode is Legacy or MBR, which is the old form of Bios and is not capable of Secure Boot.

    If you have a Windows 8 system capable of secure boot, which would include any add on video cards, you should be able to turn on Secure Boot and Disable the CSM and be able to boot. Windows 8 should still boot if CSM is enabled, since it is not required for Windows 8 to have to be set to Secure Boot. If you want to boot Windows 7 in UEFI mode, you would have to enable the CSM.

    Having said that, it should be noted there are many ways OEMs are implementing the Secure Boot option. Your Bios Setup may have different options.

    It can be confusing, so when posting back, give the model of your system and check to see if you can find the CSM and/or Secure Boot options in the Bios.

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