Interrupt

In digital computers, an interrupt is a request for the processor to interrupt currently executing code (when permitted), so that the event can be processed in a timely manner. If the request is accepted, the processor will suspend its current activities, save its state, and execute a function called an interrupt handler (or an interrupt service routine, ISR) to deal with the event. This interruption is often temporary, allowing the software to resume normal activities after the interrupt handler finishes, although the interrupt could instead indicate a fatal error.

Interrupts are commonly used by hardware devices to indicate time-sensitive electronic or physical state changes that require attention quickly. Interrupts are also commonly used to implement computer multitasking and system calls, especially in real-time computing. Systems that use interrupts in these ways are said to be interrupt-driven.

History

Hardware interrupts were introduced as an optimization, eliminating unproductive waiting time in polling loops waiting for external events. The first system to use this approach was the DYSEAC, completed in 1954, although earlier systems provided error trap functions.

The UNIVAC 1103A computer is generally credited with the earliest use of interrupts, in 1953. Earlier, on the UNIVAC I (1951) "Arithmetic overflow either triggered the execution of a two-instruction fix-up routine at address 0, or, at the programmer's option, caused the computer to stop." The IBM 650 (1954) incorporated the first occurrence of interrupt masking.