SYS$DIAGNOSTICS.SYS is an optional hardware diagnostics partition
    found on various OpenVMS I64 system disks. It is comprised of a
    FAT partition, potentially containing various diagnostics files.

    The location of this file must be registered in the bootblock
    structures using the DCL command SET BOOTBLOCK or by invoking
    the sys$setboot.exe image. If the file is deleted, then the
    bootblock must also be updated by invoking SET BOOTBLOCK or
    sys$setboot.exe.

    This section contains both an example and a detailed description.