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  1.    30 Mar 2016 #21
    Join Date : Oct 2015
    Posts : 954
    Windows 10 Pro X64


    Normally the boot menu will show both the EFI and the non EFI boot when you boot say a W10 USB stick. You then choose whether to boot the UEFI or standard model.
    That's correct for machines that support both legacy bios and EFI and are set to CSM in bios.
    If that's the case then disabling secure boot should allow a cd/dvd or whatever bootable media that is EFI agnostic to boot.

    In case of an operating system it will then also configure the system as MBR if the chosen destination disk is within MBR limitations.

    IOW, if the bios is set to use EFI then it should come to no surprise that media created to boot in legacy bios mode won't boot at all regardless of how secure boot is set in that bios.
    Of course you can create media that can boot both ways but not with optical media that already exists.
    USB sticks are so much easier and faster than optical drives even USB 2.0

    So, yes, changing the bios to legacy or CSM and disabling secure boot ( you can re-enable it again after the install has finished) will allow to boot from these media.
    However, there are some caveats if OP has other media that is EFI boot only as these now won't boot either unless the bios is set to compatibility mode (AKA CSM) and so on.

    Also, if OP later on upgrades to W10, after all MS is shoving it down your throat anyway, he'll end up with a MBR install once again which definitely has it's restrictions.

    The workaround is then to make install media and do a clean install in EFI mode, convert the HD to GPT etc.

    Either way, there are n variations on this theme thinkable but, and this is just IMHO, I'd install W7, upgrade to W10 asap and then do a clean install in EFI mode and forget about all the old stuff.

    I'd advise OP to dig in some literature on EFI/UEFI and CSM which makes it much easier to understand all these kinds of little problems that are easy to solve once you understand how it all works.

    Hope this helps,
      My System SpecsSystem Spec

  2.    30 Mar 2016 #22
    Join Date : Feb 2016
    Posts : 54

    Thanks for the info
      My System SpecsSystem Spec

  3.    30 Mar 2016 #23
    Join Date : Oct 2013
    NW Florida
    Posts : 6,105
    Windows 10 Enterprise and Pro/Windows 7 Enterprise/Linux Mint

    If you set Secure boot to disabled and CSM to Auto, it will boot either. I used to boot Windows 10 in UEFI and Windows 7 in MBR. However, you are correct if you choose UEFI DVD/CD it will install in UEFI Mode. If you boot the DVD in just the name of the DVD drive it will install in MBR Mode. At least that's the way it is on my Asus X99 board.
      My System SpecsSystem Spec

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