It's created when a hard drive is partitioned, but it's not located within a partition. This means non-partitioned storage mediums, like floppy disks, don't contain a master boot record.

How to convert MBR to GPT partition on Windows 11 Note: Before you convert an MBR partition to GPT, backup your data for safety. You can learn here how to make an image backup in Windows 11. 1.