BIOS Disk Drive Motor Status
 bit set to indicate condition
  Bit Description
  --- ----------------------------------
  0   A: Motor on (floppy 0)
  1   B: Motor on (floppy 1)
  2	 Motor on (floppy 2)
  3      Motor on (floppy 3)
  4&5 Currently selected drive number
  6   RESERVED
  7   Write in progress