User or task state v.s. supervisor.

    As OS and systems become more complex, 
      support introduced into the cpu (added instructions and functions)

      Designed to be accessed only by the OS.

      And often called the supervisor state.

      User tasks expect these functions to be available and consistent.
 
      Code written for this cpu state are part of the kernel.
  
    When user task requires access to the system, such as file access, 
      it will invoke a publicly known special routiine. On Intel systems,
        this is accessed through the software interrupt table pointers 
        found in the 1st 1K of memory.

      OS receives the request.

      Suspends the task.

      Switches to supervisor mode.

      Performs the requested system function.
        Tranfering data between device and work area of the user task.

      And restarts the task from where it made the request.
 
   If user task attempts to access the function or hardware directly or 
     run one of the superivor mode cpu instructions,
        the CPU and OS act to block access.

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