VMS Help INSTALL, ADD, Qualifiers, /SHARED  *Conan The Librarian (sorry for the slow response - running on an old VAX)

       /SHARED=[NO]ADDRESS_DATA
       /NOSHARED

    Installs the file as a shared known image and creates global
    sections for the image sections that can be shared. An image
    installed shared is implicitly installed open.

    When you use the ADDRESS_DATA keyword with the /SHARED qualifier,
    P1 space addresses are assigned for shareable images. With the
    assigned addresses, the Install utility can determine the content
    of an address data section when the image is installed rather
    than when it is activated, reducing CPU and I/O time. A global
    section is created to allow shared access to address data image
    sections.