VMS Help PASCAL, Input Output, General, OPEN, Access Method  *Conan The Librarian (sorry for the slow response - running on an old VAX)

  The 'access_method' is a  value  that  specifies  the  component
  access  method  to use.  The possible values include SEQUENTIAL,
  DIRECT, and KEYED.  The DIRECT access method  is  equivalent  to
  random  access  by  relative component number.  The KEYED access
  method is equivalent to random access by key.   The  default  is
  SEQUENTIAL.