To use the existing Windows 10 installation on a UEFI computer, you need to first convert legacy BIOS to UEFI. Here’s a simple way to do it.
If you bought a new computer, it is very likely that it is running on UEFI over the Legacy BIOS. In case you don’t know, UEFI is low-level software that runs right before the main operating system and connects the hardware, its firmware to be specific, with the operating system. In addition to connecting the hardware to Windows, it also validates the connected hardware and runs the bootloader to start Windows in the first place. Since the UEFI is pre-installed by the motherboard manufacturers, you don’t have to deal or bother with it. It just works in the background and hands over the control to Windows once the initial process is complete.
The older computers mainly used BIOS as the low-level software. When compared to UEFI, BIOS is pretty basic due to its many limitations. For example, it cannot boot high capacity hard drives, cannot initialize multiple hardware at the same time, it only supports 1 MB of storage space for its executable, etc.
To deal with all this, BIOS is eventually replaced by UEFI. In fact, almost all the modern systems in the past few years use UEFI. However, for compatibility sake, some systems include Legacy BIOS mode out of the box. The problem is, UEFI is not backward compatible with legacy BIOS. So, if you’ve installed Windows 10 on a legacy BIOS system, you cannot then change to UEFI and expect Windows 10 to boot up.
In those cases, you need to first convert Windows 10 from BIOS to UEFI and then switch to UEFI on the motherboard. Though sounds complicated, it is pretty easy to do. Just follow the steps as is and you should be good.
Check These Before Converting
Before moving any further, make sure you meet all the conditions below. If you did not meet any one or all of the conditions, stop right there and make sure you meet them.
- Windows 10 should not be encrypted with BitLocker or any other encryption software.
- The Windows 10 installation drive should not have more than four partitions (include the installation partition). If you are using a sperate dedicated drive for Windows 10, like an SSD, then you are good to go.
- You should not be dual-booting.
- You should be running Windows 10 1803 or higher. Check the Windows version.
Note: The conversion process cannot be undone once started. So, create a full backup of your system just to be safe.
Steps to Convert Legacy BIOS to UEFI
Open the start menu, search for “Command Prompt”, right-click on it and select “Run as administrator” option. In the Command Prompt window, execute the below command.
mbr2gpt /convert /allowfullOS
As soon as you execute the command, Windows starts the BIOS to UEFI conversion process. If the command is successful “Conversion completed successfully” message.
Now, reboot the system, boot into BIOS and select UEFI firmware. Once you do that, Windows 10 will boot normally. If you don’t switch your firmware from BIOS to UEFI after converting, you cannot boot into the operating system.
In Case of Errors
If you see errors like “cannot be converted” or “mbr2gpt failed” then it is possible that one or more of the above-listed requirements are not met. Or, your system isn’t compatible with BIOS to UEFI conversion due to hardware or software limitations. If that’s the case then it is better to install Windows 10 in UEFI mode directly. This eliminates the tedious troubleshooting process.
Hope that helps. If you are stuck or need some help, comment below and I will try to help as much as possible.
Thank you so very much! I’ve not restarted the system yet but I did get a successful message. However after the message it said:
MBR2GPT: Conversion completed successfully
Call WinReReapir to repair WinRE
MBR2GPT: Failed to update ReAgent.xml, please try to manually disable and enable WinRE.
Don’t know how important WinRE is but I’m gonna look it up before rebooting. Thank you so much!
So WinRE wasn’t enabled and I tried enabling in in admin command prompt and got this message:
C:\Windows\system32>reagentc /enable
REAGENTC.EXE: Unable to update Boot Configuration Data.
I’m gonna try rebooting anyway. I feel like a recovery program, while helpful, isn’t integral to a working OS.
Fingers crossed!
It worked. My computer has flawlessly made the change thanks to you.
Hey not sure this question is totally about your procedure, but here goes. Recently I was in the boot section and switched it from uefi, to legacy, been quite simetime since I messed around in or to do with bios, and have no way of resetting it to uefi now? any ideas on what I might do its a win 10 laptop made by acer.
Thanks in advance Dar
Hi Darlene,
Unfortunately, I don’t have an Acer laptop with me. So, I can’t check if the option is available or not. But, most of them have a toggle or dropdown menu to switch between Legacy BIOS or UEFI mode in the BIOS settings.
I tried enabling in in admin command prompt and got this message:
MBR2GPT will now attempt to convert the default book disk.
If conversion is successful the disk can only be booted in GPT mode.
These changes cannot be undone!
MBR2GPT: Attempting to convert disk 0
MBR2GPT: Retrieving layout of disk
MBR2GPT: Validating layout, disk sector size is: 512 bytes
Disk layout validation failed for disk 0
it failed to process. Can you recommend me any solution.
Just so you know the effect of posting information. I had two aunts that purchased computers that were refurbished and sold with legacy systems. They work from home due to covid and their jobs sent them external drives that needed UEFI. The first one was told that she needed to purchase an entire new computer. The second was on hold for 2 hours with HP before calling me.
I got them both up and they both are working. Thanks…
I have a Intel 570 chip mb with gen 11 Intel processor. System Windows 10 running in bios mode on MBR M2 drive with old graphics card that is not UEFI capable. I want to remove old video card, enable the on processor graphics, change the M2 drive to GPT and convert Windows 10 to UEFI.
When I remove the graphics card and connect to the display port on the motherboard I get a no bootable drive found in bios setup and can’t go any further. The 570 chip doesn’t allow me to use the on board graphics with an MBR boot drive or in BIOS mode. It only works with GPT drive and UEFI mode.
Should I convert Windows 10 to UEFI, shut down, remove the old graphics card, restart and convert drive to GPT then reboot?
I’m afraid I’m going to get to a dead end where I can’t go forward and I can’t go backwards either. I don’t want to reinstall Windows.
Tested this in VMware Workstation 17.5 with a Windows Server 2019 Datacenter install.
The Server 2019 ISO will not boot if you select UEFI in the Firmware Type Advanced option. The workaround is to select BIOS as the Firmware Type, once Server 2019 is installed and you are on the desktop, install (or reinstall) the latest VMware tools (download it directly from their site here https://packages.vmware.com/tools/releases/latest/windows) then reboot. Once back on the desktop follow BashKarla’s command (as administrator command prompt) mbr2gpt /convert /allowfullOS and do a shutdown NOT reboot. Once Server 2019 is shut down, go back to the VM’s Advanced settings and change the Firmware Type to UEFI, click OK to apply the setting and then boot your VM normally. Tested on Server 2016 Datacenter X64 and Server 2019 Datacenter X64 under VMware. If you are going to install the Server Software directly on your computer, same concept applies: Go into the BIOS of your computer, change from UEFI to Legacy or BIOS if the option is there, finish your install, reboot and then run her command. After you ran her command, reboot into your BIOS and change the Boot type to UEFI.