Int 15 Fn D4  - Later Ps/2s - Get Physical Fixed Disk Drive Number (selec  [B]

   AH = D4h
   DL = logical fixed disk drive number

Return: AH = return code (see #0461)
   CF set on error
   CF clear on success
       AL = physical fixed disk drive number

(Table 0461)
Values for return code:
 00h   success
 01h   specified logical drive number is invalid
 80h   function not supported (on PCjr and PC)
 86h   function not supported