How to convert Legacy to UEFI Without Data Loss (Simpler Method)
I previously had a tutorial for this at https://www.youtube.com/watch?v=Qk6_K9hVu_k but is was fairly complicated. This is a simplified process.
Please note that this method has been tested only for 64bit installations.
1. Download gpt-fdisk (gdisk) for Windows.
2. Copy the binary to a known location.
3. Boot into Windows Recovery Environment.
– If you don’t have one, download Windows10ISO from: https://www.microsoft.com/en-in/software-download/windows10ISO
– Create a bootable USB by following https://www.youtube.com/watch?v=Q8gQuYekACU or by burning the ISO to a DVD.
4. Shutdown Windows and boot using this media (Legacy or UEFI Mode).
5. Get to the command prompt. Either by pressing Shift+F10 or by navigating to it.
6. Go to diskpart and find out the disk identifier for your Windows installation.
sel disk X
7. Navigate to the location where gdisk binary is kept and type:
gdisk -l X: (Replace X with the disk number)
This will list out the partitions available in the disk. Make sure this is the one your want to convert.
8. Now, convert the partition table from MBR to GPT.
Type w to write changes. Press Y whenever prompted.
9. Type the following commands:
sel disk X (Replace X with the disk number)
# Now we make some space for our EFI partition
# Note the partition number of the partition which you want to shrink
sel par X (Replace X with the partition number)
# You may delete the System Reserved partition and replace it with the EFI partition. To do that, type:
# sel par X (Replace X with the System Reserved Partition)
# del par override
# The shrink command is not required if you do the above two commands.
# I’ll just go ahead and shrink. 500MB extra doesn’t matter to me 😀
shrink desired = 200 minimum = 200
# The following commands are common:
create par efi size = 200
format fs = fat32 quick # Format this with fat32 file system
assign letter = Z:
9. Copying boot files.
Find out the partition in which Windows is installed. Note, the partition letter here might be different than the partition letter you see in Windows. Perform dir X: on each partition letter you think can have the Windows installation and confirm X. Then type:
bcdboot X:Windows /l en-us /s Z: /f ALL
10. Done. Now reboot in UEFI mode.
Let’s check if we have indeed booted in UEFI or not!!
Type msinfo32 in run and hit enter.
Windows 7 Users Please Note: For Win7 users, one can either use a Win8 or Win10 USB/DVD, or use the newer version of bcdboot.exe from https://drive.google.com/file/d/0B8d4Lb_KJbfdNHdtUWE4eUhZOG8/view?usp=sharing
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