Switch from BIOS to UEFI and convert disk to GPT (Windows 10)

On Windows 10, you can use the MBR2GPT command line tool to convert a drive using a Master Boot Record (MBR) in the partition style GUID Partition Table (GPT), which allows you to switch correctly da Basic Input / Output System (BIOS) a Unified Extensible Firmware Interface (UEFI) without changing the current installation and without having to delete the data stored on the drive.
Put it in simpler words, using a small integrated tool in Windows 10 called MBR2GPT, we can quickly convert disk partition type from MBR to GPT. This change favors the switching from BIOS to UEFI, which is easier to use and also more useful. While before this operation required a fresh installation of Windows 10, now, thanks to this tool, everything remains as it is and nothing is deleted on the converted disk.
About what the BIOS does, as already written in a specific guide, it is enough to know that it is an essential program of every computer that is loaded by a special chip on the motherboard and which serves for the connection between hardware and software. The BIOS has been around for many years, it is still widely used, but it has many limitations such as the inability to manage partitions with space greater than 2 TB.

For this reason the BIOS has evolved into UEFI, the new firmware that replaces the old BIOS and introduces numerous additional features, including support for partitions greater than 2 TB and then also faster times for boot, sleep, recovery and shutdown. It also unlocks many of the new security features available on Windows 10, such as "Secure Boot" to protect the computer boot process from malware, "Device Guard" to control access to apps, and "Credential Guard "can help prevent unauthorized access to computer data attacks.
To use UEFI on any modern PC with Windows 10 64Bit (32-bit versions are excluded) and therefore have a faster, more stable and more secure system, you need to convert the disk drive from MBR style to GPT, which has become easy to do and harmless.
  1. How to convert a disk from MBR to GPT on Windows 10
  2. How to change the firmware mode from BIOS to UEFI

How to convert a disk from MBR to GPT on Windows 10

To do this delicate operation on the PC disk, up to a year ago a complete data backup and a fresh reinstall of Windows was required. Now the command line tool MBR2GPT simplifies this process and allows you to change the style of partitions in minutes. The conversion is done by adding the GPT components to the MBR partition, without modifying the existing partition and keeping the data intact.

Check the style of the MBR or GPT partition

Keep in mind that usually, when installing Windows 10 from scratch, the choice should be to start in UEFI mode. However, if you have upgraded from Windows 8.1 or Windows 7 to Windows 10 or if you have installed Windows 10 on a PC set to the traditional BIOS, then you need to convert the drive to correctly change the system firmware settings from the BIOS to UEFI.
Before changing the system configuration, you can check if the system is set to MBR or GPT with these steps:
  • Right click on the Start menu and choose Disk Management.
  • In Disk Management, click with the right mouse button on the box marked Disk 0 (or the disk where Windows 10 is installed) and select the Properties option.
  • Go to the Volumes tab and see if the partition style is MBR o GPT. If it is GPT, go to step 2 of this guide, otherwise proceed with the conversion.
  • Press Cancel.

NOTE: Before changing the partition style, you should check the support website of the computer or motherboard manufacturer to find out if the hardware includes support for UEFI (if it is a recent model it certainly supports it, otherwise better check carefully ).

Converting MBR Partition Style to GPT (Recommended)

To convert a drive using MBR to GPT on Windows 10, follow these steps:
  • Open Settings
  • Go to Update and security.
  • Go to Restore.
  • Press the Restart Now button under the "Advanced Startup" section.
  • Upon restart, click Troubleshoot
  • Click on Advanced Options.
  • Click on Command Prompt.
  • Then select the administrator account and log in.
Type the following command to verify that the drive meets the requirements and press Enter
mbr2gpt /validate
If after this command appears a message like "Disk layout validation failed for disk 0", then the conversion cannot be done (see below on possible problems)
The mbr2gpt.exe command is located in the "System32" folder inside the "Windows" folder. If you want to see all available options, use the mbr2gpt /? .
Now, to convert the drive from MBR to GPT, write the command and press Enter:
mbr2gpt / convert
Once done, press the close button in the upper right corner of the console and shut down the computer.
After completing the steps, several actions will occur, including validating the drive and creating an EFI system partition (ESP). UEFI boot files and GPT components will be added to the partition, then the MBR2GPT tool will update the boot configuration data (BCD) and the previous letter will be added to the drive.

Converting MBR to GPT from the Windows 10 desktop

The MBR2GPT tool was designed to work offline in the recovery environment, but you can use it even when Windows 10 is fully loaded, although it is not recommended.
To convert an MBR to GPT drive on Windows 10, open the Start menu and search for the command prompt. Right click on the prompt to run it as administrator.
Type the following command to validate the drive and press Enter:
mbr2gpt /validate /allowFullOS
To convert the drive from MBR to GPT, write and run:
mbr2gpt / convert / allowFullOS
Once the steps are completed, the tool will try to shrink the main partition and switch it from MBR to GPT.

Return codes MBR2GPT

When executing the conversion command, the return code must be 0 if all went well. In case of errors, a different number appears depending on the type of error. The list of codes and errors is as follows:
  • 1 User canceled the conversion.
  • 2 Internal error.
  • 3 Initialization error.
  • 4 Invalid command-line parameters.
  • 5 Error on the geometry and layout of the selected disk.
  • 6 One or more volumes on the disk is encrypted.
  • 7 Geometry and layout of the disk don't meet requirements.
  • 8 Error while creating the EFI system partition.
  • 9 Error installing boot files.
  • 10 Error while applying GPT layout.
  • 100 Successful conversion, but some boot configuration data didn't restore.

MBR2GPT important details and possible problems

MBR2GPT's command line tool works to convert a traditional hard drive (HDD), solid state drive (SSD), and even an M.2 drive with any version of Windows 10, but you need to run the tool from a computer running Windows 10 version 1703 or later (version 1809 recommended).
Using this tool, you cannot convert drives running Windows 8.1 or Windows 7, only Windows 10.
When using a drive that uses BitLocker file encryption, you must suspend the encryption before proceeding with the conversion.
Finally, while drives using the MBR style can have up to four primary partitions, the drive you want to convert cannot have more than three partitions, as additional allocation is required to create the UEFI system partition.
If there are two recovery partitions that were created by upgrading to Windows 10 from Windows 7 or 8, you need to delete at least one of them to proceed with the MBR to GPT conversion. This can be done easily with a partition manager such as AOMEI Partition Assistant.

How to change the firmware mode from BIOS to UEFI

After converting the drive using a GPT partition style, the device will no longer boot correctly until you enter the motherboard firmware to switch between BIOS and UEFI.
When the PC is turned on, you must then press the key to access the BIOS, usually one of the function keys (F1, F2, F3, F10 or F12) or the ESC key or the Delete key, depending on the manufacturer of the PC or the motherboard.
In the firmware interface, find the "Boot" or Boot menu and enable the UEFI option. Save the changes and the device should boot up correctly.

Check the style of the GPT partition

To verify that the computer is using the GPT partition style, right click on the Start menu to open Disk Management, then right-click on Disk 0 or Disk 1 (the one where Windows 10 is installed), go to the Volumes section and check that the partition style is that GUID Partition Table (GPT) .
The last thing to do is check if the device is using UEFI firmware mode.

Verify UEFI firmware

To verify that the computer is using UEFI firmware mode, open the Start menu and search msinfo32 . Then open the System Information utility and on the System Resources summary tab, look for the BIOS mode which should no longer be Legacy, but UEFI.

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