UEFI / Legacy BIOS Mess and Windows Update

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 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?

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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:



Apologies if that’s upside down, seems a bit unpredictable with an iPad.

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.

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.

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.

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.