Generally Windows will not touch files not generated by itself on an EFI partition. You can have multiple distinct EFI binaries and they will coexist.
]]>Windows is on a separate drive, and I can boot by selecting the Windows drive as a boot drive in BIOS.
You could install https://wiki.archlinux.org/index.php/REFInd - it will autodetect BIOS Windows installs on on external drives if you set it to in refind.conf (scanfor biosexternal).
]]>The rest of the issue sounds like it deserves attention from a Windows forum.
]]>I also have a (very rarely used) fully licensed install of Windows 10.
Whilst the original Arch installation was built for UEFI boot, I must have done something and it fell back to BIOS boot. When I reinstalled, it is, again UEFI boot. Because it wad previously BIOS, I installed Windows as BIOS boot, too.
Now I'm back to UEFI, I can't chainload Windows from GRUB. I know that Windows can be converted to UEFI boot without re-installing (though not the end of the world if I have to, and not certain I would even bother if this tunrs out to be problematic).
Windows is on a separate drive, and I can boot by selecting the Windows drive as a boot drive in BIOS. BIOS is set up to boot both UEFI or BIOS.
The Windows bootloader is also installed on it's own dedicated drive, separate from the drive where GRUB is installed.
If I convert Windows to UEFI, will this interfere with GRUB in these circumstances, or will it leave GRUB and the EFI partition that resides on my Arch drive alone until I configure GRUB to chainload?
If the latter, I'll go ahead and convert. If the former, not sure I can be bothered.
The only reason I kept Windows around was my other half is a Windows users, and not tech savvy, so I don't want to force her to use Arch if it can be avoided. If I must, she will either use her laptop, or have to learn.
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