One for each partition, plus one more at the beginning of the disk: https://en.wikipedia.org/wiki/Volume_boot_record https://en.wikipedia.org/wiki/Volume_boot_r

One for each partition, plus one more at the beginning of the disk: https://en.wikipedia.org/wiki/Volume_boot_record https://en.wikipedia.org/wiki/Volume_boot_record For instance, if you have a disk with Windows, FreeBSD, and Linux partitions, each partition has its own boot sector that loads its own boot loader, and the MBR loads one of those. (Generally it's a tiny piece of code that could come from any of the OSes that looks at which partition is marked bootable, loads the boot sector for that partition, and execs it.)