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In addition to storage protection keys, the hardware also designates certain machine instructions as restricted from general use. These are called privileged instructions (privops). These instructions can compromise the security or integrity of the computer. Examples include the instructions that set and check storage protection keys, those that start physical I/O operations, and those that set the master clock. A bit setting in the PSW register determines if a program is permitted to use the restricted instructions. Programs that are permitted to use the instructions are in supervisor state. Those that cannot are in problem state.
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