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

    (Alpha only) The Access Rights Block (ARB) compatibility option,
    the ARB_SUPPORT system parameter, is provided specifically to
    support products that have not yet been updated with the new
    per-thread security Persona Security Block (PSB) data structure.
    Changing the value of ARB_SUPPORT from 2 or 3 (the default) to
    any other value can affect the operation of these products.

                                   NOTE

       Compaq recommends that all Version 7.3 systems have the
       ARB_SUPPORT parameter set to 3 (the default). Do not change
       the ARB_SUPPORT parameter to any other value until all
       products dependent on the ARB and associated structures
       have been modified for the new environment.

    The following table describes ARB_SUPPORT parameters.

    ARB_SUPPORT
    Parameter      Value    Behavior

    ISS$C_ARB_     0        The obsolete kernel data cells are not
    NONE                    maintained by the system. Fields are
                            initialized to zero (or set to invalid
                            pointers) at process creation.

    ISS$C_ARB_     1        The obsolete kernel data cells are
    CLEAR                   cleared (or set to invalid pointers)
                            when the code would have set up values
                            for backward compatibility.

    ISS$C_ARB_     2        The obsolete cells are updated with
    READ_ONLY               corresponding security information stored
                            in the current PSB when a $PERSONA_ASSUME
                            is issued.

    ISS$C_ARB_     3 (de-   Data is moved from the obsolete cells to
    FULL           fault)   the currently active PSB on any security-
                            based operation.

    ARB_SUPPORT is a DYNAMIC parameter.