512 bytes of the hard disk (e.g. first 512 bytes of /dev/hda) and contains the partition table. There is one MBR per hard disk. Only the first 446 bytes of the MBR contain booting code; the remaining bytes are the partition table. Thus the first 446 bytes of the MBR can be copied from the old disk to the new disk, since MBR code is quite generic (e.g. stock DOS/Windows). The famous DOS "FDISK /MBR" command just overwrites the first 446 bytes of the disk with a stock MBR. Partition table: a listing of all the partitions on the disk, including extended partitions (containing logical drives). The partition table provides the essential mapping of partitions to locations on the disk. The partition table is independent of actual disk contents, but without the correct mapping your disk is unreadable. It is a bad idea to copy partition tables between disks since any difference in partition size or layout will render the copy useless. Note that the partition table is stored within the 512 bytes of the MBR. Boot sector(s): Contains code that starts the operating system, the first 512 bytes of each partition. While there is only one MBR per disk, there is a boot sector for each partition (e.g. /dev/hda1). Dual boot installations typically rely on a boot menu selector pointing towards one of several boot sectors. With multiple operating systems on a single disk, each operating system will have its own boot sector on its own partition. Backing up