In
computer science, hierarchical protection domains, often called protection rings, are a mechanism to protect data and functionality from faults (
fault tolerance) and malicious behaviour (
computer security). This approach is diametrically opposite to that of
capability-based security.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 within the architecture of a
computer system. This is generally hardware-enforced by some
CPU architectures that provide different
CPU modes at the
firmware 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 the CPU and memory.
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