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Microsoft has added a handy tool that was missing from the earlier versions of Windows and even some older versions of Windows 10. The MBR2GPT tool allows Windows 10 users to convert Legacy BIOS to UEFI without reinstalling Windows 10.

You can call the MBR2GPT tool using the command prompt, and two commands later you have switched from Legacy BIOS to UEFI.

Which is Better: Legacy BIOS vs UEFI

BIOS (Basic Input/Output System) is a piece of code that your microprocessor needs to boot after you press the computer’s power button. BIOS first appeared a long time ago and worked perfectly. However, BIOS had some limitations.

For example, BIOS uses Master Boot Record (MBR) to define a maximum partition capacity of 2.2 TB. Hardware developments over the past decade and a half justified a new firmware. Then came UEFI (Unified Extensible Firmware Interface).

UEFI, like BIOS, is low-level software that your computer runs when you press the power button and before you boot the operating system. UEFI is more robust and removes restrictions associated with BIOS.

For example, UEFI supports partitions up to 9 ZB, offers faster boot time and offers security features such as ‘Secure Boot’.

Preparing to Convert Legacy BIOS to UEFI

You need to get a few things in order before we talk about changing BIOS from Legacy to UEFI.

Check your BIOS version

Check if you are currently using the outdated BIOS. You don’t want to go through the whole process only to find out that you are using UEFI all the time.

Open the Disk Management app to check which BIOS version you are using. Search Creating and formatting hard drive partitions in the Start menu and open the Best match† This will take you to the Disk Management app.

In the app, right-click the drive where you installed Windows and select Properties

Next, you want to check the style of your disk partition to confirm whether you are using the Legacy BIOS or UEFI. If you are using BIOS, your disk partition style is MBR. If you are already using UEFI, the disk partition style is GPT.

You can check the disk partition style under the volumes tab in Properties. Search Partition style below Disc Information

Check your Windows version

The MBR2GPT tool is available on Windows 10 version 1703 and later. Before starting the process, make sure you have the correct version by searching for winner in the Start menu and open the Best match. The new window that opens shows the version on the second line.

Legacy BIOS to UEFI Conversion Requirements

Assuming you’ve verified that you’re using the Legacy BIOS, there are a few other things to check and, in some cases, change.

  1. Make sure that the target drive (ie the Windows drive) has three or fewer partitions (drive C, D, etc. are all partitions). You can view the partitions by pressing Win + R and run diskmgmt.msc† If you see more than three partitions, you must merge or delete the partitions.
  2. If you have encrypted the target drive with BitLocker, it will disrupt the conversion process. Since Windows does not convert an encrypted disk, you must disable BitLocker before starting the conversion.
  3. After conversion, you will not be able to boot into Windows until you change the motherboard firmware settings from Legacy BIOS to UEFI. Take a short tour of the firmware and look for the setting that allows you to switch between BIOS and UEFI before starting the conversion. The process varies by manufacturer, so you may need to shop around a bit. If you can’t find the setting, use the manual.
  4. Make a preventive backup.

How to Change BIOS from Legacy to UEFI

Once you’re sure everything is in order, it’s time to use the MBR2GPT tool.

  1. Search cmd in the Start menu, right click and select Run as administrator.
  2. Your drive must meet the conversion requirements for the MBR2GPT tool in order to convert it. Check if this is the case by validating the disk with the following command:

mbr2gpt /validate /disk:0 /allowFullOS

If the disk you want to convert is not disk 0, replace 0 with the correct disk number.

If your drive does not meet the conversion requirements, you will see an error message. For example, the following error resulted from validating a USB drive.

  1. If the validation is successful, run the following command to start the conversion:

mbr2gpt /convert /disk:0 /allowFullOS

Just let the conversion take a few seconds.

  1. Restart your PC and go to your motherboard firmware to change the settings. Assuming you already know how to enter the BIOS before starting the process, it should only take a few seconds. In most cases, you will see an option to select boot mode under the Boot tab in your firmware.
  1. Boot into Windows.
  2. Check if you have successfully converted the partition using the same process you used before. Go to the Disk Management app, right click on the converted drive, select PropertiesVolumeand this time around the Partition style should be GUID Partition Table (GPT)

Enjoy your modernized BIOS

UEFI comes with many features. Since most modern systems use UEFI, it is only natural to want to convert Legacy BIOS to UEFI. Well, you’re all set. Fortunately, you didn’t have to reinstall Windows either.

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