MBR

The MBR is the master boot record. It occupies the first 512 bytes of your hard drive. When the computer boots up the BIOS loads the MBR and then jumps to it.

The MBR is located on the first physical sector of your hard drive, and unless you're running stuff like FreeBSD with a dangerously dedicated filesystem, it contains the magic bytes 0x55AA at the end, a partition table and usually some simple code which is loaded onto 0000:7C00h at bootup, after which your BIOS will do a JMP FAR to the previously mentioned address. Usually, this code will load another boot sector which loads your kernel and off you go