ABSTRACT
In the design of a simple computer (ASC), we assumed one input device and one output device transferring data in and out of the accumulator using a programmed input/output (I/O) mode. An actual computer system, however, consists of several input and output devices or peripherals. Although the programmed I/O mode can be used in such an environment, it is slow and may not be suitable, especially when the machine is used as a real-time processor responding to irregular changes in the external environment. Consider the example of a processor used to monitor the condition of a patient in a hospital. Although the majority of its patient data gathering operations can be performed in a programmed I/O mode, alarming conditions such as abnormal blood pressure or temperature occur irregularly, and detection of such events requires that the processor be interrupted by the event from its regular activity. We discuss the general concept of interrupt processing and interrupt-driven I/O in this chapter.
