Int 2F Fn 4A10  - Smartdrv V4.00+ - Get Device Driver For Drive            [c]

   AX = 4A10h
   BX = 0007h
   BP = drive number (00h=A:)

Return: DL = unit number within device driver
   ES:DI -> device driver header for drive (see #1332)

Note:  this function is also supported by PC-Cache v8.0.
   this call is reported to always return the driver header of the
     standard block driver (A:-C:+) for SmartDrive v5.00 from MS-DOS 6.2

See Also: AX=4A10h/BX=0000h,AX=4A11h/BX=0003h,AX=4A11h/BX=0004h