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.