The operating system image, or kernel, is the collection of software comprising the image files (unix and genunix) and the modules loaded at any instant in time. The system will not function without a kernel to control it.
The kernel is loaded by the boot(1M) command in a machine-specific way. The kernel may be loaded from disk, CD-ROM, or DVD (diskfull boot)
or over the network (diskless boot). In either case, the directories under /platform and /kernel must be readable and must contain executable code which is able to perform the required kernel service. If the -a flag is given,
the user is able to supply different pathnames for the default locations of the kernel and modules. See boot(1M) for more information on loading a specific kernel.
If the kernel name is not explicitly specified, then on systems capable of supporting the 64-bit kernel, the boot program will attempt to load the 64-bit kernel in preference to the 32-bit kernel by default. See boot(1m).
The moddir variable contains a colon-separated list of directories that the kernel searches for modules. moddir can be set in the /etc/system file. The minimal default is /platform/platform-name/kernel:/kernel:/usr/kernel, but this default they be overridden by a specific platform. It is common for many systems to override the default path with:
where platform-name can be found using the -i option of uname(1), and hardware-class-name
can be found using the -m option of uname(1).
The kernel configuration can be controlled using the /etc/system file (see system(4)).
genunix is the platform-independent component of the base kernel.