Why change the type code of a hard disk partition? Here’s how it all started. Ventoy is an open source tool to create bootable USB drive for ISO/WIM/IMG/VHD(x)/EFI files. There is a problem, when it create an EFI partition. But there’s a problem, Ventoy creates an EFI partition, formatted as FAT16, and the partition type code is 0700 (correctly it should be EF00). On macOS, since the EFI partition is automatically mounted, if two USB flash drives are inserted at the same time, the second one will not be mounted correctly. After doing some searching, I chose GPT fdisk. It is open source software (GPL) and cross-platform, supporting Linux, macOS, Windows.