Requested system device cannot be identified after trying to repair my boot

Hello Freddie Harvey,

The "Requested system device cannot be identified" error during bootrec /rebuildbcd often stems from a missing or corrupted System Reserved partition on MBR disks, which holds essential boot files like bootmgr and the BCD store—without it, Windows can't locate the boot configuration for your C: drive. Since you're on an MBR setup (not EFI/GPT) with just Primary and Recovery partitions, and you've ruled out data loss, we can rebuild the boot environment on your C: partition itself or create a small System Reserved without converting to GPT, using safe commands from the Windows 10 ISO recovery prompt. This has worked for many similar cases without wiping data, but back up important files if possible via Command Prompt.

Key Background on MBR Boot Structure

On MBR disks for Windows 10 (BIOS/Legacy mode), the System Reserved partition (typically 100-500MB, hidden, NTFS) stores boot files and marks the drive active. Your setup lacks this, likely from a custom install or deletion, causing bootrec to fail as it can't identify the "system device." The good news: We can use bcdboot to recreate boot files directly on C: (making it active), bypassing the need for a separate reserved partition if space allows. Avoid GPT conversion tools like MBR2GPT here, as they require EFI and could complicate your MBR setup further.

Step-by-Step Repair from Command Prompt

Boot from your Windows 10 ISO as you're doing (select Repair > Troubleshoot > Command Prompt). Run these as admin—type exactly, pressing Enter after each. First, identify drives with diskpart to confirm C: is your Windows partition (look for the large NTFS volume with Windows folder).

Launch Diskpart and Prepare:

text
diskpart
list disk  (Note your main disk number, e.g., Disk 0)
select disk 0  (Replace 0 with your disk)
list partition  (Confirm Part 1 is Primary ~C:, Part 2 Recovery)
list volume  (Assign letter if needed: select vol X (Windows vol), assign letter=C)
exit

This ensures we're targeting the right drive. If C: isn't assigned, the above fixes it.

Mark C: as Active (Makes It Bootable):

text
diskpart
select disk 0
select partition 1  (Your Primary/ C: partition)
active
exit

Exit diskpart. This sets the MBR active flag on C:, so BIOS points there for boot.

Repair MBR and Boot Sector:

text
bootrec /fixmbr
bootrec /fixboot  (If it says "Access denied," run: bcdboot C:\Windows /s C: /f ALL first, then retry)

/fixmbr rewrites the Master Boot Record. /fixboot repairs the boot sector on C:. If /fixboot fails, the bcdboot command recreates it.

Rebuild BCD Store on C::

text
bcdboot C:\Windows /s C: /f ALL

This copies boot files (bootmgr, BCD) from C:\Windows to the root of C:, rebuilding the store without a separate partition. The /s C: targets C: as the system partition, /f ALL ensures BIOS/MBR compatibility. If successful, you'll see "Boot files successfully created."

Scan and Rebuild BCD (Now It Should Work):

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bootrec /scanos
bootrec /rebuildbcd  (Type Y or A when it finds installations)

/scanos detects Windows installs. /rebuildbcd should now identify C: properly and add it to the boot menu without the error.

Verify and Exit:

text
bcdedit /enum  (Should list your Windows entry without errors)
exit

Restart (remove ISO) and test boot. If it enters Windows, run CHKDSK C: /F /R from an admin Command Prompt inside OS for good measure.

If You Need a Separate System Reserved Partition

If the above fails (e.g., space issues on C:), shrink C: to create a 350MB reserved partition without data loss:

In diskpart: select disk 0, select partition 1, shrink desired=350 (creates unallocated space).

Then: create partition primary, select partition 3 (new one), format fs=ntfs quick, active, assign letter=S.

Exit diskpart, then: bcdboot C:\Windows /s S: /f ALL (points boot to S:).

Run bootrec commands again. This recreates the classic structure, but only if you have ~350MB free on C:.

Additional Tips and Warnings

No Data Loss: These commands only touch boot sectors/files, not your personal data on C:. But if C: is failing hardware-wise, consider imaging with Macrium Reflect Free from another PC.

BIOS Settings: Ensure BIOS is in Legacy/CSM mode (not UEFI), boot order prioritizes your HDD first. Disable Secure Boot if enabled.

If Still Stuck: The error might indicate multiple disks—disconnect extras. Or, use EasyBCD (free tool) from a working Windows PC to repair BCD externally, or boot to Safe Mode if accessible (F8 during boot).

Common Pitfall: If your drive has errors, run chkdsk C: /f first in recovery CMD.

This should get you booting again—I've fixed similar MBR boot woes this way countless times. If you hit a specific error during steps or share diskpart output, paste it here for tweaks.

Best regards,

Jerald Felix