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.

This article was originally published on June 24, 2010

Webopedia Staff
Webopedia Staff
Since 1995, more than 100 tech experts and researchers have kept Webopedia’s definitions, articles, and study guides up to date. For more information on current editorial staff, please visit our About page.

Related Articles

Human Resources Management System

A Human Resources Management System (HRMS) is a software application that supports many functions of a company's Human Resources department, including benefits administration, payroll,...

How To Defend Yourself Against Identity Theft

Almost every worldwide government agency responsible for identity theft issues will tell you the same thing: The first step to fighting identity theft is...

Infographic

An infographic is a visual representation of information or data. It combines the words information and graphic and includes a collection of imagery, charts,...

Phishing

What is phishing? Phishing is a type of cybercrime in which victims are contacted by email, telephone, or text message by an attacker posing as...

Remote Desktop Software

Remote desktop software gives businesses tools to use their company computers and resources...

Gartner

Gartner is a world-renowned information technology (IT) consultancy and advisory firm that conducts...

Pipedrive

Pipedrive is customer relationship management (CRM) software designed for sales. The software focuses...