Caution!

This method is extremely dangerous. Clean install with UEFI is safer.

Use at your own risk.

UEFI provides you some advantages like faster boot. So in this article, you can get how to change the boot method without losing any data.

Prerequisites.

1. Windows installation CD
2. gptgen
3. Minitool Partition Wizard

In this article I assume that you use your disk as a whole one partition without any smaller partitions like 100MB system partition. In this picture, I assume that your disk is like the disk at very bottom. If your disk is like highlighted, see this article.

Select the disk that has windows installation, and Click Move/Resize Partition button in Operations group on the left.

Subtract 228MB from Partition Size and input at Partition Size. And push 228MB at Unallocated Space Before and press OK.

Press Apply at Top-left corner in the Main window, and Yes in Apply Changes? window.

Then it will ask if you want to restart, then press Restart Now.

After restarting, open cmd as Administrator and cd to gptgen directory. Type:

gptgen -w \\.\physicaldrive(Disk number you got from Minitool)

After the operation, it can show you BSOD or not. Then restart.

Boot to Windows Installation CD and press Repair your computer

Press Troubleshoot.

Press Advanced options.

 Press Command Prompt.

Run diskpart.

diskpart

And see list of disks.

list disk

Find your disk.

  Disk ###  Status         Size     Free     Dyn  Gpt
———-  ————-  ——-  ————  —  —
Disk 0    Online        238 GB           0 B        *
Disk 1    Online        372 GB           0 B        *
Disk 2    Online        298 GB        228 MB    *

Only one disk has 228MB of free space. That’s Disk 2.

select disk 2

Create UEFI boot partition.

create partition EFI size=100 offset=1
format quick fs=fat32 label=”System”
assign letter=S
create partition msr size=128 offset=103424

Then press

list volume

And find the volume

  Volume ###  Ltr  Label      Fs    Type       Size     Status          Info
——–  —  ———-  —-  ———  ——-  ————  ——–
Volume 0     C   Windows     NTFS  Partition         237 GB  Healthy            Boot
Volume 1         SYSTEM      FAT3  Partition         100 MB  Healthy            System
Volume 2                     NTFS  Partition         450 MB  Healthy            Hidden
Volume 3     D   Projects &  NTFS  Partition         372 GB  Healthy
Volume 4     E   새 볼륨        NTFS  Partition         297 GB  Healthy
Volume 5     S   SYSTEM      FAT3  Partition         100 MB  Healthy            Hidden

We know the volume we finding is Volume 4 by size. So press

select volume 4
assign letter=C

Exit from diskpart.

exit

Lastly create boot partition data with

bcdboot c:\windows /s S: /f UEFI

Then restart and set UEFI boot setting in BIOS.