Bitfields for TI Professional PC drive type byte:
Bit(s)	Description	)
 0	drive A is double-sided
 1	drive A has 80 tracks instead of 40
 2	drive B is double-sided
 3	drive B has 80 tracks instead of 40
 4	drive C is double-sided
 5	drive C has 80 tracks instead of 40
 6	drive D is double-sided
 7	drive D has 80 tracks instead of 40
Note:	the type for drive A is determined by motherboard switches; the
	  remaining drives' types are set from a table in IO.SYS
SeeAlso: #03205