Hardware Interrupts

Some events, especially input activity, can not wait for the processor to finish doing other things before responding to the event. As a simple example, if the user presses a key on the keyboard but the processor does not get around to inputting from the keyboard until the user has hit another key, the initial key value would be lost.

Polled I/O

One of the oldest forms of handling asynchronous input requirements was by means of a technique called "polling". "Asynchronous" means not at specific time intervals, and, in this case, basically means not at a time controllable by the computer system's processor or by a program within the computer system.

The Interrupt Concept

An alternative to polling is to make the device responsible for letting the main processor know when it has some I/O requirement.

Processor Requirements for Interrupt Processing

Example: IBM PC Interrupt Processing