The occurrence of an event is usually signaled by an interrupt from either the hardware or the software.

  • Hardware
    • Hardware may trigger an interrupt at any time by sending signal to the CPU, usually by way of the system bus.
  • Software (called Trap)
    • Software may trigger an interrupt by executing a special operation called a system call.
    • The Trap could be, e.g., division by zero, or invalid memory access

Return Address

  • Before the interrupt
    • Before enter the interrupt, the return address will be stored on the system stack.
  • After the interrupt
    • After the interrupt is serviced, the saved return address is loaded into the program counter, and the interrupted computation resumes s through the interrupt had not occurred.

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