Interrupt is an action to change statement of CPU.

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External Interrupt

• Power Fail Interrupt
  When the power supply is shut down, It raise Interrupt to CPU.
  It can prevent CPU is down.
  
  
• I/O Interrupt
  When I/O devices need CPU help, It raise I/O Interrupt.
  For example, when user logs in, CPU changes the work for efficiency.
  When user complete the login, I/O device wants CPU to come back.(context switching)
  So, I/O device call Interrupt to CPU.
  
  
• Timer Interrupt
  It raises Interrupt at time’s intervals, which means CPU can work different tasks in the interval.
  For example, when eternal loop is happened, Normally it using CPU until it finishes.
  But, Timer Interrupt can put CPU into different tasks even though eternal loop is working.

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Internal Interrupt

• Exception Interrupt
  When CPU can’t deal with some commands, CPU call Interrupt itself.
  And then, CPU goes to another task.
  
  
• SVC (SuperVisor Call)
  Application calls SVC Interrupt, which calls OS to access data, because Application cannot access data.
  SVC commands Kernal, Kernal mode = Supervisor mode.