Understanding Exception Handling

Exception handling involves a basic distinction between interrupts and exceptions.

• An interrupt is an asynchronous event and is not associated with the instruction that is executing when the interrupt occurs.
• An exception is a synchronous event and is directly caused by the instruction that is executing when the exception occurs.

The computer hardware generally uses the same mechanism to report both interrupts and exceptions. The machine saves and modifies some of the event's state and forces a branch to a particular location. When decoding the reason for the machine interrupt, the interrupt handler determines whether the event is an interrupt or an exception, then processes the event accordingly.