Two special cases of External Interrupts are Non-Maskable Interrupts and External Controller Interrupts. Non-Maskable Interrupts are used to request critical operating system services. NMIs are assigned external interrupt vector number 2. External Controller Interrupts are used to service Intel 8259A-compatible external interrupt controllers. ExtINTs are assigned locally within the processor to external interrupt vector number 0.
Faults are synchronous with respect to the instruction stream.
The processor completes state changes that have occurred in instructions prior to the faulting instruction. The faulting and subsequent instructions have no effect on machine state. Faults are IVA-based interruptions. Traps are synchronous with respect to the instruction stream. The trapping instruction and all previous instructions are completed.