Ring 0

Ring 0 is one of the privilege levels in which an x86 processor can operate at any time. The others are rings 1, 2 and 3. Of these most of the operating systems including Linux use only two levels, namely Ring 0 and Ring 3. Ring 0 is the highest privilege level and is the level at which the operating system kernel runs (kernel mode). Ring 3 is the lowest privilege level and is the level at which user applications are run.

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Ring 0 is also the title of a Japanese film directed by Tsuruta Norio. See Ring 0 (movie).