External interruptions are produced by peripheral devices, for example keyboards, printers, communication cards, etc. They are also produced by coprocessors. It is not achievable to disable external interruptions.
These interruptions are not sent thoroughly to the CPU, but quite they are sent to an integrated circuit whose function is to exclusively handle this kind of interruptions. The circuit, called PIC8259A, is controlled by the CPU using for this manage a series of communication methods called paths.