VSI Pascal makes  distinctions  between  external  and  internal
  files.   An  internal  file has a name in a directory and exists
  outside the context of a VSI Pascal program.  An  internal  file
  has  no  name  and  is  not  retained after the program finishes
  execution.

  A file declared in the program heading is external  by  default.
  A  file  declared  in a nested block is internal by default.  To
  change the default for internal files, call the  OPEN  procedure
  or   specify  a  filename  on  the  EXTEND,  RESET,  or  REWRITE
  procedures.   The  file  is  then  considered  external  and  is
  retained  with the specified name after the program has finished
  execution.  If you open an internal file with the EXTEND, RESET,
  or REWRITE procedure, the file remains an internal file.