DOS Default/Predefined File Handles

	 0 - Standard Input Device - can be redirected (STDIN)
	 1 - Standard Output Device - can be redirected (STDOUT)
	 2 - Standard Error Device - can be redirected (STDERR)
	 3 - Standard Auxiliary Device (STDAUX)
	 4 - Standard Printer Device (STDPRN)

See the following  INT 21h  Handle related function calls:

	INT 21,3C  Create file using handle
	INT 21,3D  Open file using handle
	INT 21,3E  Close file using handle
	INT 21,3F  Read file or device using handle
	INT 21,40  Write file or device using handle
	INT 21,41  Delete file
	INT 21,42  Move file pointer using handle
	INT 21,43  Change file mode
	INT 21,45  Duplicate file handle
	INT 21,46  Force duplicate file handle
	INT 21,56  Rename file
	INT 21,57  Get/set file date and time using handle
	INT 21,5A  Create temporary file (3.x+)
	INT 21,5B  Create new file (3.x+)
	INT 21,67  Set handle count (3.3+)
	INT 21,68  Flush buffer (3.3+)

	- STDIN, STDOUT and STDERR can be redirected
	- maximum number of files available to all DOS processes at one
	  time is defined by the FILES=N statement of CONFIG.SYS
	- maximum number of files available to an application is N-3 where
	  N is derived from the CONFIG.SYS FILES=N statement minus the
	  count of handles used by other processes
	- INT 21,67 can be used in DOS 3.3+ to increase the number of file
	  handles for an application to greater than 20;  the max handle
	  count is still limited by the value of FILES= in CONFIG.SYS file
	- An application can increase the maximum allowed file handles in
	  DOS 3.0-3.2 by copying the open file table located through offset
	  34h in the PSP to another location.  All unopened slots must be
	  initialized to FF and the values at PSP offsets 32h and 34h must
	  be updated to reflect the new values.
	- see	SFT   INT 21   INT 21,52   INT 21,67