Interrupt Request

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What Does Interrupt Request Mean?

An interrupt request (IRQ) is an asynchronous signal sent from a device to a processor indicating that in order to process a request, attention is required. A hardware IRQ is induced by a hardware peripheral or device request, whereas a software IRQ is induced by a software instruction. Both result in processor status savings, and revert to serving the IRQ using an interrupt handler routine.

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Techopedia Explains Interrupt Request

Interrupts are commonly used to implement computing multitasking and effectively eliminate the requirement for the processor to sample (poll) the lines while waiting for external events.

An IRQ is served to the processor by programmable interrupt controllers (PICs), which prioritize and manage the interrupts to the processor. A well-known device in personal computer (PC) architecture is the Intel 8259A PIC, which was later supplanted by the advanced PICs (APICs) but continues to be used today.

Interrupts can be level-triggered or edge-triggered. Level-triggered interrupts indicate that the line is held by the device at an active level, triggering the interrupt until it is served. Edge-triggered interrupts indicate that the device triggers the line shortly from level 1 to 0 (or vice versa). The PIC is expected to catch this trigger and service the interrupt.

IRQ levels are allocated to devices to indicate their identities. For example, in a PC, IRQ0 through IRQ15 denote the 16 levels associated with the mouse, keyboard, serial port, sound card, floppy disk controller, and the primary/secondary advanced technology attachment (ATA) channels used for hard disk devices.

When two devices use the same level, IRQ conflicts occur. Today, USB plug and play (PnP) devices have virtually eliminated this problem.

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Margaret Rouse
Technology Expert
Margaret Rouse
Technology Expert

Margaret is an award-winning technical writer and teacher known for her ability to explain complex technical subjects to a non-technical business audience. Over the past twenty years, her IT definitions have been published by Que in an encyclopedia of technology terms and cited in articles by the New York Times, Time Magazine, USA Today, ZDNet, PC Magazine, and Discovery Magazine. She joined Techopedia in 2011. Margaret's idea of a fun day is helping IT and business professionals learn to speak each other’s highly specialized languages.