if you are using an MBR partition table then it’s stored in the drive MBR,

if you are using GPT with BIOS then it’s stored in the drive’s protected MBR

if you are using GPT with UEFI then it’s stored on the ESP

if you are chain-loading then you could have boot-data on a partition MBR, and the drive MBR.

http://askubuntu.com/questions/491082/steps-to-create-dd-image-file-from-usb-and-restore-image-to-a-different-usb

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