Explain the difference between vectored and non-vectored interrupt
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Answer:
A vectored interrupt is where the CPU actually knows the address of the Interrupt Service Routine in advance. All it needs is that the interrupting device sends its unique vector via a data bus and through its I/O interface to the CPU. The CPU takes this vector, checks an interrupt table in memory, and then carries out the correct ISR for that device. So the vectored interrupt allows the CPU to be able to know what ISR to carry out in software (memory).
A non-vectored interrupt is where the interrupting device never sends an interrupt vector. An interrupt is received by the CPU, and it jumps the program counter to a fixed address in hardware. This is literally a hard coded ISR which is device agnostic. MIPS uses this via it’s syscall instruction, which is the same instruction you use regardless what device, if it is an external event notifier (e.g. keyboard input), a completion signal (e.g. print completion), a clock interrupt to tell the CPU to allocate control to a different device, or an abnormal event indicator (e.g. power failure). The CPU crucially does not know which device caused the interrupt without polling each I/O interface in a loop and checking the status register of each I/O interface to find the one with status “interrupt created”.
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