The EXTERNAL attribute indicates a variable or routine  that  is
  assumed to be global in another independently compiled unit.

  Syntax:

     [EXTERNAL]

  or,

     [EXTERNAL(identifer)]

  or,

     [EXTERNAL('string-literal')]

  The 'identifer' is the name of  the  identifier  passed  to  the
  linker.   It  is passed in uppercase on OpenVMS systems.  If you
  omit the identifier, the name of the variable is used.

  The 'string-literal' passes a specified  string-literal  to  the
  linker unmodified.