Solved Where is the drive letter for the Windows partition?

Celery · Dec 3, 2021

This is a clean installation of Windows 11.

Where is the drive letter for the Windows partition when I boot from a USB stick?

If I want to repair the EFI system partition, I need to use the following commands.

diskpart
list volume (note the volume number for the Windows partition)
select volume # (where # is the volume number of the Windows partition)
assign letter=w
exit

bcdboot w:\windows

Bree · Dec 3, 2021

aubergine said:
diskpart
list volume (note the volume number for the Windows partition)
select volume # (where # is the volume number of the Windows partition)
assign letter=w
exit
bcdboot w:\windows

Your instructions say to note the volume number of the Windows partition, then you must assign it the drive letter W yourself before using it in the bcdboot command. You have to know what you are looking for to recognise the Windows partition.

From the size and format types....

Volume 0 = Windows partition
Volume 1 = EFI partition
Volume 2 = Recovery partition

and Volume 3 is a Windows install usb that you have just booted to a command prompt from.

Celery · Dec 3, 2021

NavyLCDR · Dec 3, 2021

aubergine said:
View attachment 15289

Not quite because you don't know for sure where the BCD was created. You should have also done:
select volume 1
assign letter=s
exit
bcdboot W:\Windows /s S: /f UEFI

NavyLCDR · Dec 3, 2021

Berton said:
Diskpart shows 4 drives on my main Win10 computer but not their drive letters, disks 1, 2, and 3 are External USB drives and Disk 0 has 2 lettered partition, C: and D: with C: being small at 150GB and D: about 780GB. Disk 0 partition C: is the boot/system/Windows drive.

Completely different situation. You ran diskpart from C:\Windows\System32 which indicates that you were booted into Windows when you ran it. In post #3, @aubergine ran diskpart from X:\Sources which indicates that they were booted into Windows PE - probably booted from a Windows installation USB flash drive.

Celery · Dec 4, 2021

But where is the drive letter for the Windows 11 partition? Today I also noticed this on a Windows 11 virtual machine. This is weird. Has anyone else noticed this? This does not exist in Windows 10 or if you have upgraded from Windows 10 to Windows 11.

Oracle VM VirtualBox ([X]Enable EFI).
This is a clean installation of Windows 11.
(see screenshot below)
I booted from a Windows 11 installation ISO file > diskpart > list volume
Where is the drive letter for the Windows 11 partition?

1 - VirtualBox - Clean installation of Windows 11.jpg

Oracle VM VirtualBox ([X]Enable EFI).
This is a clean installation of Windows 10.
(see screenshot below)
I booted from a Windows 10 installation ISO file > diskpart > list volume
The drive letter of the Windows 10 partition is displayed.

2 - VirtualBox - Clean installation of Windows 10.jpg

Celery · Dec 4, 2021

NavyLCDR said:
Not quite because you don't know for sure where the BCD was created. You should have also done:
select volume 1
assign letter=s
exit
bcdboot W:\Windows /s S: /f UEFI

But there was no error message. "Boot files successfully created."

/s <volume letter> --- Why should this be used?
/f <firmware type> --- Why should this be used?

At least for me, this is a really hard thing to understand. But if you look at Microsoft's website.

Source: BCDBoot Command-Line Options

/s <volume letter>
- Optional. Specifies the volume letter of the system partition. This option should not be used in typical deployment scenarios.
- Use this setting to specify a system partition when you are configuring a drive that will be booted on another computer, such as a USB flash drive or a secondary hard drive.

/f <firmware type>
- Optional. Specifies the firmware type. Valid values include UEFI, BIOS, and ALL.
- On UEFI/GPT-based systems, the default value is UEFI. This option creates the \Efi\Microsoft\Boot directory and copies all required boot-environment files to this directory.
- If you specify the /f option, you must also specify the /s option to identify the volume letter of the system partition.

I tested the bcdboot command without /s <volume letter> and /f <firmware type> options and commands succeeded without an error message and then the computer started normally. This is a clean installation of Windows 11.

I booted from the Windows 11 installation USB flash drive in UEFI boot mode (marked UEFI in the boot menu) and then I run the following commands.

Recreate the EFI system partition boot files (see below).

Code:

diskpart
list volume
select volume # (where # is the volume number of the Windows partition)
assign letter=w
list volume
exit

bcdboot w:\windows

edit: (copied from another forum)
- BCDBoot copies the boot files from the Windows partition to the EFI system partition and creates the Boot Configuration Data (BCD) store in the same partition. If the volume letter is incorrect or if you boot from the Windows installation USB flash drive in Legacy BIOS mode (not marked UEFI in the boot menu), you will receive the following error message: Failure when attempting to copy boot files.

Format the EFI system partition and recreate the EFI system partition boot files (see below).

Code:

diskpart
list volume
select volume # (where # is the volume number of the Windows partition)
assign letter=w
list volume
select volume # (where # is the volume number of the EFI system partition)
format quick fs=fat32
list volume
exit

bcdboot w:\windows

NavyLCDR · Dec 4, 2021

aubergine said:
But there was no error message. "Boot files successfully created."

/s <volume letter> --- Why should this be used?
/f <firmware type> --- Why should this be used?

At least for me, this is a really hard thing to understand. But if you look at Microsoft's website.

If you run "bcdboot W:\Windows" it is going to put the boot files to boot Windows from W: drive on whichever BCD the computer booted from. Many times, especially when booted into Windows PE, the user will not know where that BCD came from. Many times when users have multiple HDDs or SSDs installed and they may not realize the computer is booting from a different drive than they thought. For example, "I upgraded my HDD to an SSD by cloning, then I either removed or formatted the HDD and now my computer won't boot!" That's because the user thought the computer was booting from the SSD, but it was booting from the HDD.

Assigning a drive letter to the system partition that you want to populate with boot files, and then using the /s switch with the bcdboot command will ensure that you are doing exactly what you thought you were doing - and not creating or adding to a BCD on some mystery location.

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