VMS Help Sys Parameters, CONCEAL_DEVICES  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    CONCEAL_DEVICES enables or disables the use of concealed devices.
    By default, this parameter is set to enable concealed devices
    (1).

    This special parameter is used by Compaq and is subject to
    change. Do not change this parameter unless Compaq recommends
    that you do so.