Bitfields for TI Professional drive type information:
Bit(s)	Description	)
 7	floppy drive D: has 80 tracks
 6	floppy drive D: is double-sided
 5	floppy drive C: has 80 tracks
 4	floppy drive C: is double-sided
 3	floppy drive B: has 80 tracks
 2	floppy drive B: is double-sided
 1	floppy drive A: has 80 tracks
 0	floppy drive A: is double-sided