What happens if I switch to UEFI mode after install Windows 10 in Legacy mode?

Question

I have installed Windows 10 on my PC using Legacy mode(I checked Bios Mode in System Infomation, and it said Legacy). Now, after I found out the many advantages of UEFI mode, such as fast booting, secure boot, etc. etc. I want my machine work with UEFI mode.

Do I need to install it again in UEFI mode? I dont want to do this because I found out from googling it that the hard drive must be wiped completely to change hard drive system from MBR to GPT to make it run in UEFI mode.

What if I directly switch to UEFI mode(without reinstalling)? Will it work without complications?

Solution

If you just change from CSM/BIOS to UEFI then your computer will simply not boot. Windows does not support booting from GPT disks when in BIOS mode, meaning you must have an MBR disk, and it does not support booting from MBR disks when in UEFI mode, meaning you must have a GPT disk.

There are ways to convert an MBR disk to GPT, such as Aomei Partition Manager, but doing so will break your system and mean that there are steps needed to fix it. Generally you will need the install media for your OS in order to repair it.

Technet has a guide on how to convert a Windows Installation from BIOS to UEFI for Win 7/8. There are a lot of steps involved and you could quite easily destroy your current data using that procedure. I would not do it without a complete backup of all the files I cared about.

Comments

[tvdo]

MBR2GPT is the official way to convert a Win10 installation.