Initial software based Multics had 64 rings, and as I recall only 8 in the hardware versions.  No more than 4 were needed in practice: 0 for root, 1 for mail (e.g. you could delete mail you&#x27;d sent to other people from their mailboxes if they&#x27;d not read it yet), 4 for normal users, and 5 for some stuff that e.g. allowed anyone to use, but was restricted at touching anything deeper in the system.<p>AMD dropped rings in their 64 bit architecture which Intel was forced to adopt, so they&#x27;re becoming a historical curiosity.