Produces a display listing the processors in the OpenVMS
    multiprocessing or single-CPU system, indicating which is the
    primary processor, which processors are configured, and which
    processors are active.

    The /SUMMARY qualifier also indicates the minimum revision
    levels required for processors in the system, which OpenVMS
    synchronization image has been loaded into the operating system,
    and whether multiprocessing is enabled. If the presence of one or
    more uniprocessing drivers in the system prohibits the enabling
    of multiprocessing, the SHOW CPU command displays a warning
    message.