Thanks again for your help. Yes, D is Disk0, and C and F are on Disk1 in Windows Disk Management. But at the Command Prompt, what was D in Windows is now C, what was C in Windows is now F, and what was F in Windows is now D. I have the Boot Manager on Disk0 (as assigned in Windows, Windows put it there because I was careless during installation, I wasn't aware what would happen). But I want it on Disk1/Partition1 instead, while the OS resides on Disk1/Partition1. Then I will disconnect the current Disk0, as I'd like to have only one disk in the system (less noise). So I would use bcdedit /set {bootmgr} device partition=X, where X should be the current partition Disk1/Partition2, as seen as by the Windows boot code. Since this is the active partition, I would have guessed that it must be C at the CMD prompt. My current BCD points to D as Disk0, but to Disk2/Partition1 as C (that's where the OS is, not the bootloader), so apparently it uses the Windows drive letter assignment partly, but not everywhere (hence making me think it is pure coincidence). So I am confused what to tell bcdedit as X.