VMS Help V73 Features, System Management Features, AlphaServer GS Series, Hard and Soft Partitions  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    Hard partitioning is a physical separation of computing resources
    by hardware-enforced access barriers. It is impossible to read
    or write across a hard partition boundary. There is no resource
    sharing between hard partitions.

    Soft partitioning is a separation of computing resources by
    software-controlled access barriers. Read and write access across
    a soft partition boundary is controlled by the operating system.
    OpenVMS Galaxy is an implementation of soft partitioning.

    The way customers choose to partition their systems depends on
    their computing environments and application requirements. For
    more information about using hard partitions and OpenVMS Galaxy,
    refer to the OpenVMS Alpha Partitioning and Galaxy Guide.