Int 2A Fn 0300  - Network - Check Direct I/o                               [N]

   AX = 0300h
   DS:SI -> ASCIZ device name (may be full path or only drive specifier--
         must include the colon)

Return: CF clear if direct physical addressing (INT 13,INT 25) permissible
   CF set if access via files only

Notes: do not use direct disk accesses if this function returns CF set or the
     device is redirected (INT 21/AX=5F02h)
   use AH=00h to determine whether the network is installed; if not,
     direct physical access is allowed
   may take some time to execute, so programs which need to check
     frequently should save the result of the first call
   this function is called by the DOS kernel on INT 25 and INT 26
   supported by PC LAN Program, LAN Manage, LANtastic, NetWare, 10NET,
     etc.

See Also: INT 13/AH=02h,INT 13/AH=03h,INT 25,INT 26,INT 21/AX=5F02h