(1) The ringer line in an early telephone cable. See
tip and ring.
(2) A privilege level in the computer. When software is assigned to a ring, it may be limited to executing certain instructions in the computer. Ring 0 has the highest privilege and can access all instructions. The operating system or the virtual memory monitor (VMM) resides in ring 0.
Applications typically reside in ring 3, which has a lower priority, and are prohibited from executing instructions that address the hardware. If an application attempts to execute a prohibited instruction, an error indication (fault) is generated. Rings 1 and 2 are available in some computers, but may or may not be used. See
virtual machine monitor.