Webopedia on Google+Webopedia on TwitterWebopedia on FacebookTech Bytes Blog
Main » Quick Reference »

What Are IRQ Numbers?

Prior to plug and play devices, users had to set IRQ values of devices manually when adding the device, such as a modem or printer, to a system. The following list of IRQ numbers specifies what each of the 16 IRQ lines are used for.

Prior to plug-and-play devices, users had to set IRQ values of devices manually when adding the device, such as a modem or printer, to a system. The following list of IRQ numbers specifies what each of the 16 IRQ lines are used for.

RQ Number
Typical Use
Description
IRQ 0 System timer This interrupt is reserved for the internal system timer. It is never available to peripherals or other devices.
IRQ 1 Keyboard This interrupt is reserved for the keyboard controller. Even on devices without a keyboard, this interrupt is exclusively for keyboard input.
IRQ 2 Cascade interrupt for IRQs 8-15 This interrupt cascades the second interrupt controller to the first.
IRQ 3 Second serial port (COM2) The interrupt for the second serial port and often the default interrupt for the fourth serial port (COM4).
IRQ 4 First serial port (COM1) This interrupt is normally used for the first serial port. On devices that do not use a PS/2 mouse, this interrupt is almost always used by the serial mouse. This is also the default interrupt for the third serial port (COM3).
IRQ 5 Sound card This interrupt is the first choice that most sound cards make when looking for an IRQ setting.
IRQ 6 Floppy disk controller This interrupt is reserved for the floppy disk controller.
IRQ 7 First parallel port This interrupt is normally reserved for the use of the printer. If a printer is not being used, this interrupt can be used for other devices that use parallel ports.
IRQ 8 Real-time clock This interrupt is reserved for the system's real-time clock timer and can not be used for any other purpose.
IRQ 9 Open interrupt This interrupt is typically left open on devices for the use of peripherals.
IRQ 10 Open interrupt This interrupt is typically left open on devices for the use of peripherals.
IRQ 11 Open interrupt This interrupt is typically left open on devices for the use of peripherals.
IRQ 12 PS/2 mouse This interrupt is reserved for the PS/2 mouse on machines that use one. If a PS/2 mouse is not used, the interrupt can be used for other peripherals, such as network card.
IRQ 13 Floating point unit/coprocessor This interrupt is reserved for the integrated floating point unit. It is never available to peripherals or other devices as it is used exclusively for internal signaling.
IRQ 14 Primary IDE channel This interrupt is reserved for use by the primary IDE controller. On systems that do not use IDE devices, the IRQ can be used for another purpose.
IRQ 15 Secondary IDE channel This interrupt is reserved for use by the secondary IDE controller.






TECH RESOURCES FROM OUR PARTNERS
LATEST ARTICLES
The Problem with Statistics

We look at a few of the more troubling aspects of statistics and how these may be used to advance an agenda or skew the facts to someone's... Read More »

29 Free Android Apps for Cash-Strapped Students

From wacky alarm clocks to lecture hall tools and after class entertainment, these Android apps are a good fit for a student's life and budget. Read More »

Sharing Threat Intelligence

A growing number of startups make the sharing of threat intelligence a key part of their solutions. Read More »

STUDY GUIDES
The 7 Layers of the OSI Model

The Open System Interconnection (OSI) model defines a networking framework to implement protocols in seven layers. Use this handy guide to compare... Read More »

Network Fundamentals Study Guide

Networking fundamentals teaches the building blocks of modern network design. Learn different types of networks, concepts, architecture and... Read More »

Computer Architecture Study Guide

This Webopedia  study guide describes the different parts of a computer system and their relations. Read More »