UEFI / Legacy BIOS Mess and Windows Update

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  1. Posts : 10
    Windows 10
    Thread Starter
       #21

    NavyLCDR said:
    That will reformat your existing system partition that the computer is booting from and then create the boot files needed to boot the computer in legacy BIOS (CSM) mode. After booting in legacy BIOS (CSM) mode, then Windows upgrade should proceed because you will no longer be in UEFI mode.
    Thanks. I like the sound of this approach. I can worry about moving to UEFI in the future, if ever. As thereís already a system reserved NTFS partition, can I skip the formatting step? That way I can switch back to UEFI in the BIOS settings if thereís a problem, and it will still boot in the same way as it currently does. Would that work?

    Iíd like to understand better whatís going on at the moment please so that hopefully Iím less likely to break things in the future! I assume there are some UEFI boot files currently in the system partition and I need to replace these with the legacy boot ones?

    - - - Updated - - -

    Caledon Ken said:
    I think OP said in post #1 he set his BIOS to boot UEFI.

    Would he not have to change this back to "Legacy".

    A snippet from his manual. I did not see option for CSM Mode although "Advance Boot Options" maybe providing this functionality.

    Attachment 285907

    from here

    https://www.dell.com/support/manuals...ee3&lang=en-us
    These are my boot options:

    UEFI / Legacy BIOS Mess and Windows Update-d74edea3-0359-4164-972e-eb8b607dfa93.jpeg

    Apologies if thatís upside down, seems a bit unpredictable with an iPad.
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  2. NavyLCDR's Avatar
    Posts : 13,356
    Windows 10 Pro
       #22

    Tonkski said:
    Thanks. I like the sound of this approach. I can worry about moving to UEFI in the future, if ever. As there’s already a system reserved NTFS partition, can I skip the formatting step? That way I can switch back to UEFI in the BIOS settings if there’s a problem, and it will still boot in the same way as it currently does. Would that work?

    I’d like to understand better what’s going on at the moment please so that hopefully I’m less likely to break things in the future! I assume there are some UEFI boot files currently in the system partition and I need to replace these with the legacy boot ones?
    It's good that you have a computer that will boot from an NTFS partition in UEFI mode, as most computers will not. It's a good idea to reformat the system partition, just so you know for sure what boot files are going to be there. And if you change one option in the commands, you should be able to boot in either UEFI or legacy mode:

    Code:
    Diskpart
    select disk 0
    select partition 1
    format fs=ntfs label="SYSTEM"
    assign letter="S"
    active
    exit
    bcdboot C:\Windows /s S: /f ALL
    It's the very last option in the very last command. Changing Bios to ALL will cause boot files compatible with both UEFI and legacy to be written to the system partition. Then for the upgrade to proceed without the error it's just a matter of changing your "BIOS" settings (in your screen shot above) to boot in legacy mode.
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  3. Megahertz's Avatar
    Posts : 1,263
    Windows 7 HP 64 - Windows 10 Pro - Lubuntu
       #23

    Never seen this before. OP has a MBR drive with a active System partition and he is booting as UEFI from a partition that is not Fat32.

    Also noted that he has encrypted C: partition. Don't know where is the key conversion to open the drive so Data backup, without encryption, on an external disk is a must do.
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  4. Caledon Ken's Avatar
    Posts : 20,942
    Windows 10 Pro x64 Version 1909
       #24

    In your screen shot it also says you must enable Advance Boot Options to boot legacy.

    Actually it says "Legacy Option ROM's" need to be enabled for Legacy boot mode but that is what Advance Boot Options is.
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  5. Paul Black's Avatar
    Posts : 5,134
    Win 10 Pro 64-bit v1909 [Customised]
       #25

    Megahertz said:
    Never seen this before. OP has a MBR drive with a active System partition and he is booting as UEFI from a partition that is not Fat32.

    Also noted that he has encrypted C: partition. Don't know where is the key conversion to open the drive so Data backup, without encryption, on an external disk is a must do.
    Me neither !!!
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  6. NavyLCDR's Avatar
    Posts : 13,356
    Windows 10 Pro
       #26

    Some computers will boot from an NTFS partition in UEFI mode. Most, however, won't. MBR v. GPT does not matter for booting - but Windows expects to see a GPT drive if booting in UEFI mode from the internal drive. The USB flash drive created by Microsoft's Media Creation Tool will be MBR partitioned with a FAT32 partition that is marked as active so that it will boot in both legacy BIOS and UEFI.
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  7. Posts : 10
    Windows 10
    Thread Starter
       #27

    Thanks for everyoneís help. Iíll try the suggested approach to switching back to legacy boot when I have time over the next couple of days and Iíll report back.
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  8. Paul Black's Avatar
    Posts : 5,134
    Win 10 Pro 64-bit v1909 [Customised]
       #28

    Tonkski said:
    Thanks for everyone’s help. I’ll try the suggested approach to switching back to legacy boot when I have time over the next couple of days and I’ll report back.
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  9. Caledon Ken's Avatar
    Posts : 20,942
    Windows 10 Pro x64 Version 1909
       #29

    Good luck.
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  10. Megahertz's Avatar
    Posts : 1,263
    Windows 7 HP 64 - Windows 10 Pro - Lubuntu
       #30

    Tonkski, as you have a UEFI BIOS, why don't you make it UEFI- GPT instead of Legacy-MBR?

    - Backup your data on an external disk.
    - Uninstall Bitlocker

    Find out in witch partition is the boot manager (bcdedit /enum)
    Maybe all you have to do is to convert the first partition (system Reserved) to Fat32 and then convert from MBR to GPT

    To convert with mbr2gpt.exe
    - Boot from Win 10 installation drive, launch a CMD window and type:
    Diskpart (to enter diskpart)
    List disk (take note from the win 7 disk you want to convert)
    exit (to exit diskpart)
    MBR2GPT /convert /disk:<diskNumber>

    Brink tutorial Convert Windows Legacy-MBR to UEFI-GPT without data loss
    Last edited by Megahertz; 1 Day Ago at 18:37.
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