VMS Help CC, Language topics, Storage Class Modifiers, __align  *Conan The Librarian (sorry for the slow response - running on an old VAX)

  The __align storage-class modifier has the same semantic meaning as
  the _align keyword.  The difference is that __align is a keyword in
  all compiler modes while _align is a keyword only in modes that
  recognize VAX C keywords.  For new programs, using __align is
  recommended.