DOS Fns 01H-0cH: Low-level I/O

                                                         Compatibility: 1.0+ 
 These low-level I/O functions are given special treatment.  DOS switches
 to a special stack when calling these fns.  The idea is to allow higher-
 level fns to call these without reentrancy problems.  In particular, it is
 OK for device drivers to use fn 01H-0cH during initialization.  And popup
 TSR programs must pay special attention to when these fns are available
 and when not.

 See TSR and InDOS Flag and ErrorMode Flag and INT 24H for related details.

     See: 01H Keyboard Input
          02H Display Output
          03H Auxiliary Input
          04H Auxiliary Output
          05H Printer Output
          06H Console I/O
          07H No Echo Unfiltered Console Input
          08H No Echo Console Input
          09H Display String
          0aH Buffered String Input
          0bH Check Input Status
          0cH Clear & Input

See Also: Character I/O Functions
          DOS Functions