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Guy Harris (talk | contribs) Multics-style/Honeywell 6180-style, or x86-style, call gates aren't the only mechanism used to transfer control from a less-privileged protection domain to a more-privileged protection domain. |
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Computer operating systems provide different levels of access to resources. A protection ring is one of two or more hierarchical ''levels'' or ''layers'' of [[Privilege (computing)|privilege]] within the architecture of a [[computer system]]. This is generally hardware-enforced by some [[Central processing unit|CPU]] [[Computer architecture|architecture]]s that provide different [[CPU modes]] at the hardware or [[microcode]] [[abstraction layer|level]]. Rings are arranged in a hierarchy from most privileged (most trusted, usually numbered zero) to least privileged (least trusted, usually with the highest ring number). On most operating systems, Ring 0 is the level with the most privileges and interacts most directly with the physical hardware such as certain CPU functionality (e.g. the control registers) and I/O controllers. With the increasing prevalence of [[virtualization]], many CPUs have added another level (conceptually ring -1) for the [[hypervisor]].
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==Implementations==
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