Windows 10: Dual boot on two drives, how to separate EFI on one drive and transfer it to another?

I was fixing my friend's Hard disk drive after his broke due to corruption, and I had wiped it clean using my sister's computer. Sorry for my bad English I'll refer to my friend's disk drive as disk 0 and my sister's as disk 1 I plugged in disk 0 into my sister's pc while having disk 1 which had windows 11 OS still placed inside, since for whatever reason or I'm just stupid disk 0 couldn't be read as a standalone drive it didn't boot when I was trying to download windows 10 on it without disk 1. I then started the download process once again, everything went smoothly, though en

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Dual Booting with Windows 8.1


The procedure below will allow you to boot Windows separately or in dual boot configuration.
Here's what I recommend to do:

1. Disconnect the drive containing Windows 8.1
2. Install Windows 10 with one drive connected.
3. After step 2, reconnect the drive containing Windows 8.1
4. Boot up Windows 8.1. Open disk management and take a note of the drive letter of Windows 10 OS.
   NOTE: if you boot up Windows 10, then take a note of Windows 8.1 drive letter
5. Open Admin command prompt and type: bcdboot X:\windows where X: is the drive letter of Windows 10 (Windows 8.1 if you boot from Windows 10 in step 4)
6. Reboot the PC. You should have a dual boot screen.

NOTE: To break off the dual boot setting, Win+R->msconfig->boot and delete the none default entry on the list.

 

Can't boot from DVD drive

Is your controller in RAID/AHCI modes? If so, the DVD drive will be listed as a separate device in the list of available boot devices, not as "CDROM". Remember that when setting boot device priority. Otherwise, read the manual to see which hotkey during POST brings up the boot menu that lets you select which device to boot from. Even here, the drive will be listed separately, and not as "CDROM".

 

Dual boots from a single physical drive

OK, @churin, the next step is to try to get that second EFI system partition to boot Windows 8 directly. In a command prompt with admin run: Code:

Now, similar to my computer below:

The last partition in your list should be a 99 or 100 MB system partition, but it will have a different partition number. You want to continue in the same command prompt window with: Code:

Now reboot your computer and see if you can get that EFI system partition (Windows Boot Manager) to boot directly into Windows 8. If you can, we move on to the next steps.