The master boot record, located at the first 512 bytes of the device memory, contains partition address and size information. The Preloader and Bootloader images are stored in partitions of type 0xA2. Other items may be stored in other partition types according to the target file system format.
You can use the fdisk tool to set up and manage the master boot record. When the fdisk tool partitions an SD/MMC device, the tool creates the master boot record at the first sector, with partition address and size information for each partition on the SD/MMC.