Function 21, subfunction 8 - set used HD partition.

The HD partition defines partition of the hard disk to write with usage of obsolete file system functions and functions implicitly using the hard disk (such as subfunction 6 of function 18); at usage of functions 58 and 70 and modern syntax /HD0,/HD1,/HD2,/HD3 these functions set base and partition themselves.
Parameters: Return value: Remarks: