Windows 10 setup in Legacy BIOS mode can’t install to a GPT-partitioned disk
You’re encountering this issue because Windows 10 setup in Legacy BIOS mode can’t install to a GPT-partitioned disk, which is how your disk is currently set up (as required by Windows 11 in UEFI mode).
Two key points:
- GPT is required for UEFI boot.
- MBR is required for Legacy BIOS boot.
- You can install Windows 10 on a GPT disk, but only if you’re booting the Windows 10 USB installer in UEFI mode.
✅ Solution (Recommended): Boot Windows 10 USB in UEFI mode
You need to ensure that the USB installer is booted in UEFI mode, not Legacy BIOS. Here’s how:
1. Check your BIOS/UEFI boot options
- Reboot the computer and enter BIOS/UEFI setup (usually
F2,DEL,ESC, orF10depending on your machine). - Ensure UEFI boot mode is enabled.
- Disable Legacy/CSM Boot to force the system to boot the USB in UEFI mode.
2. Boot from USB in UEFI mode
- On boot, enter the boot menu (
F12,F9, etc. depending on your motherboard). - You should see two entries for your USB stick:
UEFI: <USB name>← Select this oneLegacy: <USB name>or just<USB name>← Don’t use this
3. Continue installation
- Now Windows 10 setup should see the GPT partition and install without error.
- Select the empty NTFS partition you created and install there.
🔁 Alternate Fix (Not recommended unless you understand the risks): Reformat disk as MBR
This would involve:
- Backing up your entire system.
- Reformatting the disk as MBR (which would break your Windows 11 installation).
- Installing Windows 10 first, then reinstalling Windows 11.
⚠️ Do not do this unless you want to erase Windows 11.
🧠 Pro Tip: Managing Bootloaders
When installing Windows 10 alongside Windows 11:
- The Windows 10 installer may overwrite the bootloader, making Windows 11 temporarily inaccessible.
- After installation, use a tool like EasyBCD or bcdedit in Windows to restore or manage dual boot.