The protection ring, also referred to as hierarchical protection domains, is the mechanism used to protect a system against failure. Its name is derived from the hierarchical structure of its levels of permission, represented by concentric rings, with privilege decreasing when moving to the outside rings. Between each ring there are special gates that allow the outer ring to access the inner ring resources in a restricted manner.
Understanding the protection ring
Architectural differences
The number and order of rings depend on the CPU architecture. They are usually numbered with decreasing privilege, making ring 0 the most privileged one. This is true for i386 and x64 architecture that use four rings (from ring...
