A reference copy directory is a directory in which CMS
  stores a copy of the latest generation on the main
  line of descent for each element in a library. (The main
  line of descent of an element consists of generation 1
  of the element and all its direct descendants; that is,
  generations 2, 3, 4, and so on.)

  The reference copy directory is not a CMS library; it is
  an OpenVMS directory associated with a CMS library. You cannot
  assign a CMS library as a reference copy directory, nor
  should it be a subdirectory of a CMS library.

  To establish reference copies, you must:

  1. Create an OpenVMS directory at DCL level (with the DCL
     CREATE/DIRECTORY command).  For new libraries, you
     may direct CMS to create the directory for you.

  2. Associate the reference copy directory with the CMS
     library:

     o  For new libraries, supply the name of the reference
        copy directory in the New Library dialog box.  If
        you would like CMS to create the library for you,
        click on the Automatically Create Directory button.

     o  For existing libraries, supply the name of the
        reference copy directory in the Modify Library
        dialog box.

  3. Associate the reference copy directory with elements:

     o  For new elements: new elements inherit the
        reference copy attribute from the library;
        that is, new elements have their reference
        copy attribute turned on by default if the
        library has a reference copy directory.

     o  For existing elements: You must set the
        reference copy attribute for existing elements;
        pull down the Modify Element dialog box and
        activate the Reference Copy option.