16h
16h - Get Partitionable Disk Count: The number of non-removable drives is returned.
17h - Map Unit Numbers to Physical Drive: The request packet unit field indicates a non-removable drive number that is zero-based. OS2DASD adds Function 80h and searches for VolCBs associated with that particular physical unit. A bit map of unit numbers associated with the physical drive is returned. The bit numbering scheme for the bit mask corresponds to 2**(unit number) in a ULONG field.