C: is the boot partition
After Windows 10 upgrade there were eight partitions. Booted into a Live USB Linux and run
gparted, then simply deleted all partitions except the required EFI partition and C: partition, and even shrunk the C: partition to make room for a dual boot later. (Note: did not move the C: partition, just shrunk it.)
At reboot, Windows 10 started just fine with just the two partitions. I even forgot and did a hybrid Windows shutdown before all this (where it saves state to speed next startup) so it started fine but showed all those old partitions for a while, crashed on disk management rescan, but next full start it was okay from then on, after making me do a diskcheck. Feels quite stable to delete all but EFI and C: when your C: is your boot partition.
Reference reserved partition being deletable, and efi partition being required.
C: is NOT the boot partition
I repeated the above on a different system where the vendor (Acer) booted from a special partition first, which wasn't my EFI or C: partitions, and Windows wouldn't start any longer, because I deleted the special vendor boot partition. Note, it did boot Windows (EFI partition worked) but couldn't find C: and had a Windows 10 version of a blue screen which is lighter blue and some sort of error about no boot partition found.
Ordinarily to fix this boot your Windows 10 recovery USB stick then pick: language
advanced options |
startup repair |
Windows 10. Except this wouldn't help because the vendor tweaked the EFI and C: partitions to not be fixable.
My fix was to boot Windows 10 recovery USB, take the options that lead you to a command prompt. There, you can try with the usual
bootsect /nt60 C: and look for Windows installations
bootrec /scanos and mine found none. Then ran
diskpart, did the usual
list volumes mine happened to be 2,
select volume 3,
remove letter C,
select volume 2,
assign letter C, to make C: where Windows is installed (it's temporary).
It showed as hidden, so to unhide it couldn't simply use
attribute volume, got a not found, ended up having to
set id=ebd0a0a2-...etc to make it a normal Data partition, then changed the attribute to not hidden. Running
attribute volume should show "no" on all four lines. At that point, C: is not hidden. Had to
attribute volume clear nodefaultdriveletter so on boot it would assign C: normally. Just for grins, changed the EFI partition to be an EFI partition (happened to be 1) with
select volume 1 and
set id=c12a7328...etc. Still shows hidden but that's okay, EFI is normally hidden.
So my partitions are not longer messed up, removed all the weirdness the vendor did to them. But still not finished, had to setup C: to boot correctly. Tried
bcdedit /enum and saw some odd boot settings in my C:, so to undo that
bcdboot C:\Windows /v. The last thing is the secret sauce.
At this point
bcdedit /enum showed more normal looking things and it booted properly.
Above, that first 301MB unallocated was the original boot partition I deleted.