When creating a Windows To Go USB drive, Rufus can use either GPT or MBR. With the MBR option, it also creates a small FAT-based EFI System Partition at the end of the drive, allowing the same USB stick to boot on both legacy BIOS and UEFI systems. Is there a standard name for this layout? Also, can an EFI System Partition be added to an existing MBR disk without converting the disk to GPT, and could it be used to hold a VeraCrypt bootloader?
3 Answers
You can create a small FAT32 partition on an existing MBR disk and mark it with the EFI System Partition type, such as 0xEF. The appropriate UEFI boot files then need to be placed in that partition. Partitioning tools such as DiskPart or GParted can generally create and identify the partition, though care is needed to avoid overwriting existing data.
This is commonly described as an MBR disk with UEFI support, or as a hybrid BIOS/UEFI boot layout. An EFI System Partition is not limited to GPT; on an MBR disk it can be represented by an FAT partition with the MBR partition type 0xEF. Rufus uses this arrangement so one drive can boot through either BIOS or UEFI.
The EFI boot files are not necessarily tied to GPT. UEFI mainly needs a properly formatted partition containing the expected bootloader files, so files from a GPT-based setup may work on an MBR disk if the bootloader supports that arrangement. However, a VeraCrypt bootloader may depend on its installation method and disk layout, so simply copying files from another disk is not guaranteed to work; it may need to be installed or configured specifically for the target drive.
So the files are often portable between GPT and MBR layouts, but VeraCrypt may still require its own installer or configuration to recognize the manually created EFI partition correctly?