Does anybody know the algorithm DOS uses to assign drive letters to partitions?

I'm working on a Windows-based install program for NetBSD and try to identify all
parts of the hard disks I've found to the user. "Disk 2 partition 3" is a lot less familiar
than "Drive D:" to him.

I do have all partition tables and a list of DOS partitions, now in what order are the
drives assigned?


Thank you,


Martin