What does setting boot drive to "BOOT" in EasyBCD do?

Harry37

Member
I'm having major problems getting my single-boot 64-bit Windows 10 Pro system to boot again. It's a hand-built desktop that has worked fine (with some exceptions) for years. The exceptions I referred to relate to situations just like this one wherein I just can't get it to boot. The error I see now and most commonly in the past is an "Inaccessible boot device" BSOD.

SUMMARY of my question: I'm using EasyBCD to edit the desktop's BCD to ensure that when I boot up, the system partition is set as the boot partition at drive letter "C:". If I set the BCD boot entry to "BOOT", just what does that do?

Full explanation: I'm guessing that there's some problem with the BCD, which is where EasyBCD 2.4 (community edition) becomes indispensable. I'm using it on my Win 10 laptop to load the BCD from the desktop's system SSD, which I've connected directly to the laptop so I can fix any problems with it (such as by running CHKDSK, and offline DISM and SFC). None of which has solved the problem.

So back to EasyBCD. Although I've been using it for many years, I've never been able to figure out what I should choose as the boot drive. Since the laptop's boot drive letter is always "C:", the two-partition desktop SSD drive are assigned D: and E:, with D: holding the Windows 10 system (release 1909). But there are some AutoIt executable scripts and a couple of other executables residing on the second partition on that SSD which are run as Startup applications, all of which expect to be present on drive letter "B:", so I change drive letter "E:" to "B:". On second thought, I see that this was a dumb idea, but I can't fix this until I can boot again. Is this the cause of the "Inaccessible boot device" error? I don't know.

In this OP, all I want to know is the question posed above: If I set the BCD boot entry to "BOOT", just what does that do?

BTW: A little while ago I purchased my third or fourth edition of EasyRE, but it doesn't fix the problem. Just FYI...

Thanks!
 

Terry60

Telephone Sanitizer (2nd Class)
Staff member
There are no drive letters in the BCD. Windows letters are virtual labels with no physical existance in the real world. If your PC is powered down (or running Linux) there are no drive letters.
When you boot Windows it will assign letters to the drives or partitions in the order that they're encountered during plug and play and map them against the drive ID in the registry unless you've previously assigned a personal letter using Disk Management in which case it will use that letter already stored in the registry map. It will also have already mapped the partition containing the OS as C during the installation setup (unless you installed Windows from a running OS rather than from the booted installation medium, in which case C is already in use and it will have mapped the OS as the next available letter)
EasyBCD spares you the effort of using the user-unfriendly ID in the BCD which is an unmemorable hash of the unique device serial number and the partition offset from the device start, by cross referencing this with the assigned letter in the registry map and allowing you to address partitions as if there were actually letters stored in the BCD.
It follows therefore that each individual OS has its own drive letter mapping and there will not necessarily be any resemblance between one and another (unless like me, you deliberately assign indentical maps manually)
Since a letter cannnot appear more than once in any system's map, if you look at the OS drive from a different PC attached to your running PC, it cannot be C but will be given the next available letter on the running OS
EasyBCD is a Windows .NET app and only works on a running OS and therefore uses the letters as seen by that OS
If you're editing the BCD of another OS you must still use the letters as seen by the running OS, not what the "dead" OS normally sees.
You don't set the BCD to "boot", there's no way to do so. That's EasyBCD telling you that the BCD is located in the normal default location i.e. the first drive in the HDD priority list in the BIOS.
You must set the "guest" BCD's entries as the host system sees the partition letters.
 

Bobbybabb

Member
Use EasyBCD to create a bootable USB : Go to BCD Deployment. Select your partition from the drop-down menu. Install BCD to USB. Allow EasyBCD to load USB bootloader. Change the name and type. Wait for EasyBCD to close! My CC Pay
 
You can assign a drive letter to your partition correctly using the Windows Terminal (aka Command Prompt). You MUST have admin privileges to this terminal/command line however. This is a very dangerous step as if you do not know what you are doing it can mess up your hard drive partitions. You can assign actual drive letters to be correctly displayed to the corresponding Volume and Partition of each disk. Each physical disk can have multiple partitions that are necessary for the Windows Operating system to function. screwing this up will make your drive unbootable but if you know what you are doing it will for certain fix this problem by assigning an actual drive letter to that specific partition.

I am using Windows 11 22H2 (version 22638.1000.0). Open up an Administrators Terminal Window. Do a search in Windows for 'Terminal App' and start it and make sure the pull-down menu is set for Administrators access under 'Command Prompt'. The keybind to use is "CTRL + ," to bring up the Settings for the command prompt and set this to admin access in the Terminal window. Here is how it looks like.

2022-12-16 04_57_17-What does setting boot drive to _BOOT_ in EasyBCD do_ _ NeoSmart Forums — ...png

One the terminal is set for admin access (it is off by default so you must set this setting), you can then use the 'DISKPART' command and 'LIST VOLUME' and 'LIST PARTITION' commands to show the partitions and volumes.

2022-12-16 05_03_55-What does setting boot drive to _BOOT_ in EasyBCD do_ _ NeoSmart Forums — ...png

You can then use the ASSIGN (HELP ASSIGN for more info) to assign an actual drive letter to be correctly ascribed to that healthy Main partitions. Each partitions does something useful to each OS disk and you CAN NOT SCREW THIS UP! Be careful here! If there are already drive letters assigned then these LOGICAL drive letters may shift as you load them their boot order around in the BIOS.

The way I have my system configured is the corresponding main drive I have booted into (C and D) will either become THE physical "C" drive if it is the main drive I am booted into. For instance the current "D" drive will actually become "C" once I boot into it. As I type this I am on the "C" drive so the alternate 445 GB drive is shown as "D" from my current "C" drive but if I boot into the 445 GB drive it will then be shown as "C" and the 1,860 GB drive will become "D". Depending on which drive I want to work in on that day. My BOOT drive will always be the 1860 GB partition regardless if I am booted into the 445 GB partition (as far as DISKPART is concerned and this software is the God drive daddy to it knows the best) since its a seperate disk and you can only have one physical BOOT partition for the entire computer.

NOTE: You just need to use these commands ONLY to assign drive letters and that is it! No other commands are required!

LIST VOLUME
...('HELP VOLUME' for more info)
LIST PARTITION
...('HELP PARTITION' for more info)
SELECT VOLUME
...('HELP SELECT VOLUME' for more info)
SELECT PARTITION
...('HELP SELECT PARTITION' for more info)
ASSIGN
...('HELP ASSIGN' for more info)

OPTIONAL:
REMOVE
...('HELP REMOVE' for more info)

Green color are safe commands to just browse but the red letter is a dangerous command if you do not know what you are doing.


You first must a.) list the volumes or partitions then b.) you must select which partition you want to work with then c.) you can assign the drive letter to that partition. You will ONLY assign a drive letter to a partition NOT THE VOLUME OR DISK! Once the [ENTER] key is pressed that partition will be set so if you reboot at this point your drive can be unbootable (if you assigned the wrong partition a drive letter). You can also unassign it back (more in the following post) to whatever it was if you screw up, but a reboot at this point is certainly a butt clincher if you are doing this for the first time.

These 2 commands are the only thing required to assign a drive letter but you MUST know which partitions do assign it to or it could make that disk unbootable. DO NOT practice this on your main boot disk. Test it on a secondary or tertiary disk first and see if it takes after you reboot. Once you get more practice with this and survive a restart (if all went well) you can practice it on your target disk (the one you want to be "B").

Type 'EXIT' to exit out of the DISKPART interface and you will be back to the terminal window and then just click the "X" in the upper corner of the window to close it fully.

There is software like Easeus Partition Manager (one I recommend but the full version may be pricey, the free version is good enough to just see the partitions graphically so you know which partition to assign the drive letter to), Macrium Reflect, AOMEI PAssist, Partition Wizard Home Edition or any freeware partition software to see the partitions visually instead of in a terminal text only in a window.

I am not typing this on my backup drive where I have all the partition software installed for recovery or I would give you a screenshot of how they look like.
I hope this helps. I know this is tough but this is certainly how the Pros do the assigning of drive letters CORRECTLY! Cheers!
 
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I found an old sample of some old recovery steps to assign a temporary drive letter of "S" I needed to do back in the day. You can use this as a reference for what I did. It is very simple once you KNOW what partition to assign the drive letter to. There are many partitions on a physicial disk and some are hidden and created by the OS. They are there for a reason to help in recovery and normal functioning. Do not tamper with them if you are unsure. You can substitute "S" for the "B" drive you want to make. I show the steps I used to create an entire partition and saved this process. The 'bootsect' is there to show you how I setup the boot partition for this temporary setup. BE CAREFUL with the 3 lines after "c:\>". You may not need to do this at all in your instance!

YES, all these commands were done under a Windows 11 terminal window environment!

DISKPART> list disk
DISKPART> select disk 0
DISKPART> list partition
DISKPART> select partition 1
DISKPART> assign letter=S
DISKPART> exit
c:\> bootsect /nt60 all /force
c:\> bcdboot c:\windows /s S: /f ALL (or /f UEFI)
c:\> diskpart
DISKPART> list disk
DISKPART> select disk 0
DISKPART> list partition
DISKPART> select partition 1
DISKPART> list volume
DISKPART> remove letter=S
DISKPART> exit
 
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