Library /sys$common/syshlp/sysmanhelp.hlb IO, SET, PREFIX, Example  *Conan The Librarian (sorry for the slow response - running on an old VAX)

  SYSMAN> IO SET PREFIX=(SYS$,PSI$,VME_)

      This example specifies the prefix names used by IO
      AUTOCONFIGURE to build the ICBM names. The prefixes are SYS$,
      PSI$, and VME_.