Boot from GPT hard disk in Legacy BIOS mode

GPT is modern and has many advantages over MBR. However, there are also some issues with GPT booting in Legacy BIOS mode. GPT is part of the EFI specification, of course it will work best in UEFI mode. But maybe it will not be compatible and can not boot up on the BIOS computer. See more here. Microsoft also does not support booting Windows on a GPT hard disk in Legacy BIOS mode.

So far, MBR is still supported in both UEFI and Legacy BIOS boot. However, there are several reasons that you must use GPT instead of MBR. MBRs only work with disks up to 2TB in size. If you have a hard disk larger than 2TB (e.g. 3TB), use the GPT format to get the full capacity of the disk.

AIO Boot now supports installing Grub2 on GPT disks including both HDD and USB. After installing Grub2, you can boot the GPT disk in Legacy BIOS mode.

Windows Boot Manager does not support booting into Legacy BIOS mode on GPT disks. AIO Boot uses wimboot to do this.

Install Grub2 with the boot partition

  1. Install AIO Boot to a partition on GPT disks.
  2. The grub-install, grub-bios-setup command on Linux and the grub-install.exe, grub-bios-setup.exe program on Windows require a boot partition on the GPT disk to install Grub2 for the Legacy BIOS mode. On Linux, this partition will be flagged as bios_grub. We will create a small partition of 1 to 10MB. You do not need to format and do not need to mount the drive letter for this partition. For USB, you can use the MiniTool Partition Wizard to create a second partition.

    USB multiple partitions
    For USB, you can use the MiniTool Partition Wizard to create a second partition.
  3. Run AIOCreator.exe, select Grub2 from Bootloaders. The tool will list the partitions that you created in step 2.
  4. Select the partition and click OK to install Grub2.

    Install Grub2 on GPT
    Run AIOCreator.exe, select Grub2 from Bootloaders.

Install Grub2 without a boot partition

This is a new feature of AIO Boot v0.9.8.1. It supports installing Grub2 on the GPT hard disk to boot in Legacy BIOS mode without creating a boot partition.

  1. Install AIO Boot to a partition on GPT disks.
  2. Run AIOCreator.exe.
  3. Select Install Grub2 (Legacy) from the Tools button. This button only appears when the current hard disk is GPT and the current drive format is FAT32 or NTFS.
    Grub2 boot GPT in Legacy Bios without UEFI
  4. Please note that you should reinstall Grub2 every time you defragment on this drive.

Good luck!



11 thoughts on “Boot from GPT hard disk in Legacy BIOS mode”

  1. Hello, I probed this, but not boot from (hd0,gpt7)/Boot/BCD. Booted from msdos from another disk. Should I make wimboot boot.wim file? How can I do it? Thanks

  2. Yes, I probed that. Copy boot.wim from windows installer sources folder to /AIO/Files/WinPE and push the “Boot WinPE via WimBoot”. After I got the installer language chooser menu. But how can I start BCD in this method for loading installed windows to (hd0,gpt8)? Maybe I need to make any method boot.wim which BCD have?

      1. I have copied windows partition to GPT disk. This is booting well from msdos partition’s BCD of another hdd. But I like boot from same disk. This was my hope.

  3. I have installed AIO boot on gpt hardisk. then I also install windows7 64x on the hard drive using dism – apply image. but the aio boot can not boot my windows. What should I do?

        1. Impossible. You try to install Clover by running AIOCreator.exe -> Bootloaders -> Clover.
          You can then boot into Grub2 and rEFInd in UEFI mode from Clover.

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