To be bootable, a COHERENT file system must contain a boot block (either boot or mboot). In addition, all hard disks must contain the master boot block mboot or an equivalent.
mboot is the master boot block for a hard- disk drive. It is compatible with, and therefore can replace, the IBM master boot block installed by the MS-DOS command FDISK. It must be installed in the first sector of the hard disk, as follows:
/etc/fdisk -b /conf/mboot /dev/at0x
/bin/sync
mboot searches its internal partition table (updated by the command ffddiisskk) for an active partition. You can select an alternate partition by pressing 0 through 7 before the system selects the active partition. If the selected partition is of non-zero size with a valid partition boot block, COHERENT executes that partition's boot block. Otherwise, the prompt
Select partition [0-7]
appear, and the system waits for you to select the partition you want.