There are two types of interrupt requests that can be initiated by hardware external to the processor:
Maskable interrupt requests initiated by hardware devices. These requests are delivered to the interrupt controller which, in turn, delivers the interrupt to the processor by asserting the INTR signal to the processor. They are referred to as maskable interrupts because the programmer may disable the processor's ability to recognize the INTR signal and may also program the interrupt controller to selectively disable recognition of interrupt requests from certain devices.
Non-Maskable Interrupt (NMI) requests issued by the chipset to signal that a serious hardware condition has been detected on the system board. These interrupts ...