How to Convert the System from Legacy BIOS mode to UEFI mode after Installing Windows*

When installing Windows, the partition style used will determine if UEFI mode or legacy BIOS mode is supported. UEFI mode is compatible with the GUID Partition Table (GPT) partition style while the legacy BIOS mode is compatible with the Master Boot Record (MBR) partition style. Most of the latest features and capabilities are only available in UEFI mode; however, there may be systems that still use the MBR partition style, which means the system is configured in legacy BIOS mode.

MBR and GPT are two different ways of storing the partitioning information on a drive. This information includes where partitions begin, so the operating system knows which sectors belong to each partition and which partition is bootable. This is why a partition style has to be chosen before creating partitions on a drive.

The instructions in this article describe how to convert the partition style from MBR to GPT in systems where the Windows operating system was originally installed in legacy BIOS mode. If you have the legacy boot option set in BIOS , it is possible that the drive partition table is MBR. If you want to install a fresh Windows operating system in UEFI mode, see the instructions in How to Configure the System in UEFI Mode before Installing Windows*.

Before following these instructions, it is highly recommended to perform a backup of your data. If you have a second disk drive with enough available capacity, you can create a system image and recover the full installation as it was before you started this procedure. Links provided to third-party tools and sites are for your convenience. We don't endorse the content, products, or services offered. We don't offer support for third-party tools.

Step 1: Confirm the operating system is installed in a MBR partition

1. Boot into Windows.
2. Open Disk Manager by pressing the Windows key and the X key simultaneously, and then clicking the Disk Manager option.
3. In Disk Manager, locate the primary system boot partition.
   
4. Right-click the disk shown as Disk x, Basic, Capacity, Online on the left.
5. Select Properties.
6. Click the Volumes tab. The partition style will be shown.

Step 2: Convert the partition style from MBR to GPT using MBR2GPT.exe

MBR2GPT.exe is a Windows utility available in Windows 10 Creators Update x64 (Version 1703, Build 10.0.15063) or later. This utility allows converting a disk using MBR partition style to GPT partition style without modifying or deleting data on the disk. However, it is highly recommended to backup your data before continuing with this procedure.

1. Open Command Prompt with administrator privileges.
2. Run the following command: mbr2gpt.exe /convert /allowfullOS
3. Restart the system and boot into the system BIOS.
4. Change the settings from Legacy BIOS mode to UEFI mode.

Alternatively, you may also run this command from the Windows Recovery Environment:

1. Boot into the Windows Recovery Environment.
2. Open Command Prompt by following these steps:
   1. Press the Windows key and the I key simultaneously to open the Windows Settings menu.
   2. Select Update & Security.
   3. Select Recovery.
   4. Select Restart now under Advanced startup.
   5. Select Troubleshoot.
   6. Select Advanced Options.
   7. Select Command Prompt.  It may prompt you to select a user account and type a password.
3. Run the following command: mbr2gpt.exe /convert
4. Restart the system and boot into the system BIOS.
5. Change the settings from Legacy BIOS mode to UEFI mode.

Alternative Step: Convert from MBR to GPT in a secondary drive (no OS installed)

If the drive is a secondary drive (data drive with no OS installed), you can use third-party applications such as EaseUS* to convert from MBR to GPT.