I am trying to install Windows 10 in legacy mode on a drive that uses MBR. I have a Windows 10 installation ISO file from which I created a bootable USB drive. However, USB drive only boots in UEFI mode, and not in legacy mode (I alternated between the two options in the BIOS menu). When the Windows installation process is started in UEFI mode, it cannot install Windows to a MBR drive. Hence I need to create a bootable USB drive that can start in legacy mode. Is this a limitation of the ISO file that I am using? I have tried many different utilities (Rufus, UNetbootin, etc..) to create the bootable USB.
If this is the case, where can I obtain a Windows 10 installation ISO (I have a license key) that can be used to create a legacy bootable USB drive?
Best Answer
Rufus does not create dual BIOS+UEFI USB disks by default – it has an explicit selection for that. Therefore if the USB stick successfully boots in UEFI mode, it is UEFI-only and you need to select "BIOS (CSM) mode" in Rufus.