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My laptop has Windows 8.1 currently running, and I plan to install Windows 10. The 8.1 that I am currently running is on Disk 0. I would like to convert Disk 0 to MBR, so that I can use EasyBCD to add a boot option in the boot manager. Questions:

  1. Is it possible to change from GPT to MBR since I am going to perform the process on Disk 0 and the fact that my Windows 8.1 is also included in Disk 0?
  2. Can I create a boot option for Windows 10 without converting to MBR?
  3. A detailed explanation on how to convert from GPT to MBR without data loss(preferred), if not, then how?

I will be using a third-party application software called Paragon Partition Manager, since it is free of cost, pictures below: https://prnt.sc/vmmoq6

https://prnt.sc/vmmp5a

Any queries, please type it in the comments section.

Thanks.

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  • The third-party application only supports converting MBR to GPT it cannot convert GPT to MBR. Additionally, it’s not necessary to use a third-party application, to do the conversion from MBR to GPT MBR2GPT exists on Windows 10
    – Ramhound
    Nov 20, 2020 at 14:57
  • The application also listed changing from GPT to MBR, and BTW, I have formatted my PC and changed from GPT to MBR. Well, the disk engine ran during boot and formatted it to MBR
    – user1223472
    Nov 23, 2020 at 3:25

2 Answers 2

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It's important to note that you will be changing two things at once: not just the disk from GPT to MBR, but also the system boot process from UEFI mode to BIOS mode.

Overall I wouldn't recommend doing this at all. Most likely it will be more work than just using Windows' own bcdedit to add the correct boot entry, with no practical gain.

Can I create a boot option for Windows 10 without converting to MBR?

Very likely that installing Windows 10 will just do that automatically. But note that both operating systems must be installed in the same boot mode (i.e. if you have Windows 8 running in UEFI mode, make sure to start Windows 10 installer in UEFI mode as well).

Is it possible to change from GPT to MBR since I am going to perform the process on Disk 0 and the fact that my Windows 8.1 is also included in Disk 0?

Yes, but not using Windows built-in tools – and as mentioned, it won't be enough to convert the disk itself, you will also have to rebuild the Windows bootloader as well.

To convert the disk itself you will need the "gptfdisk" program (aka gdisk). Easiest is to run it from a Linux live CD/USB. Disks with up to 4 partitions can always be converted; there might be issues if you have 5 or more partitions.

Afterwards, you will need to switch to BIOS boot mode in the firmware settings, then switch Windows itself to have a BIOS-mode bootloader instead of the UEFI-mode one that it had installed previously.

To do this, you'll need to delete the "EFI System Partition" that held the original Windows 8 bootloader and create a NTFS-formatted "Microsoft System Partition" in its place. Then boot from a Windows installation USB, and use bcdboot to install a new bootloader along with a new BCD.

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  • Hey, well, thanks for the answer, but I had already formatted my PC and now I am running windows 8.1 and windows 10 dual-boot. Things were confusing me in your answer, and I decided to go with the hard-method. But anyways, I appreciate you answering my question. Thanks! :)
    – user1223472
    Nov 23, 2020 at 3:11
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The bcdedit makes often a lot of problems. I have to manage various computers (some with UEFI and some with BIOS) with the same windows installation. My way is, I maintenance a single UEFI/GPT installation in a VMWare Machine (free of charge). To install it on other computers, I boot this VM-machine in cd-rom mode, using a clonezilla iso. Clonzilla offers to save an image of the whole system ( the virtual machine), e.g. on an external usb-drive or on a network resource (e.g. samba). Then you can use clonezilla an a usb stick on the computer to clone the virtual machin on this computer. After reboot, windows is looking for hardware specific drivers and after 30 min everything is done. If I need the same installation on a BIOS computer, a have a second windows installation in VMWare as bios computer (e.g. use a win10 iso and force VMWare to boot with BIOS, look in VMWare documentations). This has an small MBR partiotion for booting. I use clonezilla on the uefi installation, save only the second = windows partition as image. Than, I replace the windows partition of the BIOS installation with the image from uefi partition and widows boots without any trouble. A good idea is running chkdsk /f of the bios installation after overwriting it with the partition from the uefi installation.

In short, you can simple replace the windows partition from a (may be temporary) MBR installation with the clonzilla image from the windows partition (only partition, not full disk image) of a GPT installation. This remains all data and the whole installation. An only free software was used.

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