I submit that &quot;supervisor&#x2F;user&quot; isn&#x27;t an implementation of &quot;rings&quot;, plural (and it&#x27;s got to predate Multics by a lot, but I can&#x27;t quickly prove that), and that SMM is something entirely different.  Hypervisors and there use really aren&#x27;t comparable to Multics Rings.<p>A couple of minutes with Google only found hints that confirm my memory WRT to AMD64 and rings, and&#x2F;or Intel not copying a segmentation feature added to later versions of AMD&#x27;s chips.