Interrupts

• What is the role of interrupts in a computer system?

  Interrupts signal the processor that other devices or applications require attention.
• How does the fetch-decode-execute cycle work in relation to interrupts?

  The cycle includes an additional step to check for new interrupts after executing instructions.
• What analogy is used to explain the concept of an interrupt?


  An interrupt is like a student raising their hand to ask a question.
• What happens when an interrupt is received by the processor?

  The processor stops executing its current program to run the interrupt service routine.
• What is the interrupt service routine?

  It is a program with its own set of instructions that needs to be executed to handle the interrupt.
• How does the processor know where to find the first instruction of the interrupt service routine?

  The contents of the program counter are changed to point to the address of the first instruction of the interrupt.
• What is the purpose of the stack in handling interrupts?

  The stack saves the current values of registers so the processor can return to the previous program after handling the interrupt.
• What happens when an interrupt occurs while another interrupt service routine is being executed?

  The current interrupt service routine is suspended, and its register contents are pushed onto the stack.
• How does the stack handle multiple interrupts?

  The stack allows for multiple interrupt service routines to be suspended and resumed in the correct order.
• What is the priority of interrupts compared to standard programs?

  Interrupts always have a higher priority than standard programs.
• What is an example of a situation where an interrupt is necessary?

  When a computer becomes unresponsive and requires a task manager to be opened.
• What are the steps involved in the fetch-decode-execute cycle including interrupts?

  1. Fetch the instruction.

  2. Decode the instruction.

  3. Execute the instruction.

  4. Check for any new interrupts to be handled.
• What are the key components of the processor that hold data during the execution of programs?

  • Program Counter (PC)
  • Current Instruction Register (CIR)
  • Memory Address Register (MAR)
  • Memory Data Register (MDR)
• What happens to the register values when an interrupt is received?

  • Current register values are copied to a stack frame.
  • The stack frame is pushed onto the stack for later retrieval.
• How does the stack facilitate the handling of nested interrupts?

  • Each interrupt service routine's register values are pushed onto the stack.
  • The stack allows retrieval of the previous values in the correct order after each interrupt completes.
• What are typical categories of interrupts that might be relevant for exams?

  • Hardware interrupts
  • Software interrupts
  • Timer interrupts
  • I/O interrupts