In OpenVMS, executive and user images are loaded into dynamically
    assigned address space. To help you associate a particular
    virtual address with the image whose code has been loaded at
    that address, SDA provides several features:

    o  The SHOW EXECUTIVE command

    o  The symbolization of addresses, described in the Using_Symbols
       help topic

    o  The READ command

    o  The SHOW PROCESS command with the /IMAGES qualifier

    o  The MAP command

    The OpenVMS executive consists of two base images, SYS$BASE_
    IMAGE.EXE and SYS$PUBLIC_VECTORS.EXE, and a number of other
    separately loadable images. Some of these images are loaded on
    all systems, while others support features unique to particular
    system configurations. Executive images are mapped into system
    space during system initialization.

    By default, a typical executive image is not mapped at contiguous
    virtual addresses. Instead, its nonpageable image sections
    are loaded into a reserved set of pages with other executive
    images' nonpageable sections. The pageable sections of a typical
    executive image are mapped contiguously into a different part
    of system space. An image mapped in this manner is said to be
    sliced. A particular system may have system parameters defined
    that disable executive image slicing altogether.

    Each executive image is described by a data structure called a
    loadable image data block (LDRIMG). The LDRIMG specifies whether
    the image has been sliced. If the image is sliced, the LDRIMG
    indicates the beginning of each image section and the size of
    each section. All the LDRIMGs are linked together in a list that
    SDA scans to determine what images have been loaded and into
    what addresses they have been mapped. The SHOW EXECUTIVE command
    displays a list of all images that are included in the OpenVMS
    executive.

    Each executive image is a shareable image whose universal
    symbols are defined in the SYS$BASE_IMAGE.EXE symbol vector.
    On initialization, SDA reads this symbol vector and adds its
    universal symbols to the SDA symbol table.

    Executive image .STB files define additional symbols within
    an executive image that are not defined as universal symbols
    and thus are not in the SYS$BASE_IMAGE.EXE symbol vector. You
    can enter a READ/EXECUTIVE command to read symbols defined in
    all executive image .STB files into the SDA symbol table, or a
    READ/IMAGE filespec command to read the .STB for a specified
    image only.

    To obtain a display of all images mapped within a process,
    execute a SHOW PROCESS/IMAGE command. See the description of the
    SHOW PROCESS command for additional information about displaying
    the hardware and software context of a process.

    You can also identify the image name and offset that correspond
    to a specified address with the MAP command. With the information
    obtained from the MAP command, you can then examine the image
    map to locate the source module and program section offset
    corresponding to an address.