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Thread: Can an EFI-type GRUB2 Launch a legacy Windows bootloader?

  1. #1

    Default Can an EFI-type GRUB2 Launch a legacy Windows bootloader?

    I have an EFI-type GRUB2 installation on my internal hard disk that is used to boot various Linux distros, a.o. Tumbleweed. The laptop BIOS is set to use UEFI boot mode. The internal HD is GPT-partitioned. All Linux are 64 bits.


    Additionally, I have an external hard disk (via eSATA) that is MBR-partitioned. It holds a Windows 8.1 64-bit, installed in legacy mode. Nevertheless, I can boot this legacy Windows using the laptop BIOS boot device selector at start-up without having to change the laptop BIOS setting to legacy boot mode.


    I would like to know whether I can Lauch the Windows legacy bootloader from my EFI-type GRUB2 (chainload +1 to the system-reswrterved partition of the Windows installation??? ??? ???). I tried, but it fails.


    (A) Either this crossing the EFI / BIOS boundaries is impossible, or (b) I am doing something wrong in my 40_custom code.


    Any definitive statements wrt (a)?
    Some code (b)?

  2. #2
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    Default Re: Can an EFI-type GRUB2 Launch a legacy Windows bootloader?

    I'm pretty sure that cannot be done.

    It's a "you cannot switch horses in the middle of the stream" kind of problem.

    Your BIOS has two different interfaces, one for UEFI and one for legacy. So you can switch at the start of boot. But neither interface has a way of telling the BIOS to switch to the other interface half way through booting.

    There are web pages on how to convert a legacy Windows install to a UEFI windows. You can try googling to find details. I do not know whether that is a safe thing to do. What you are currently doing seems like the safest option.
    openSUSE Leap 15.3; KDE Plasma 5.18.6;

  3. #3

    Default Re: Can an EFI-type GRUB2 Launch a legacy Windows bootloader?

    Nice to meet you again, and thanks. I figured there’s a „wall“ between the two that cannot be crossed, but looked for confirmation.

    Side remark wrt converting from legacy to UEFI: My laptop is quite old (eSATA...) but pretty fast, and its BIOS/UEFI has a half-baked UEFI. It can boot UEFI only from HD and optical drive, but not from USB and eSATA. Nevertheless, I keep liking it.

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