Other oddities is there was no MBR or on disk
partition tables for
large drives. The partition info was kept in the DPH/DPB inside the BIOS.
I
suspect that DRI considered that area to be an issue left to the
implementor. We certainly allowed two OS-es to reside on the same
drive by simply implementing our own partition table scheme and
making the hard disk access routines aware of it. MS-DOS scarcely
does anything much more elegant.
Back then two OSs on a disk would have been truly extravagant.