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

    (Alpha Galaxy platforms only) The Shared Memory Cluster
    Interconnect (SMCI) system parameter SMCI_PORTS controls initial
    loading of SYS$PBDRIVER. This parameter is a bit mask; bits 0
    through 25 each represent a controller letter. If bit 0 is set,
    which is the default setting, PBAx is loaded (where x represents
    the Galaxy Partition ID). If bit 1 is set, PBBx is loaded, and
    so on up to bit 25, which causes PBZx to be loaded. For OpenVMS
    Alpha Version 7.2, Compaq recommends leaving this parameter at
    the default value of 1.

    Loading additional ports allows multiple paths between Galaxy
    instances. In the initial release of the Galaxy software, having
    multiple communications channels is not an advantage because
    SYS$PBDRIVER does not support fast path. A future release
    of OpenVMS will provide Fast Path support for SYS$PBDRIVER,
    when multiple CPUs improve throughput by providing multiple
    communications channels between instances.