Updated: 04/02/2019 by Computer Hope

Short for interrupt request, an IRQ is a signal sent to the computer processor to stop (interrupt) it momentarily. IBM-compatible computers go up to IRQ 15 and are prioritized in the computer according to the importance of the device. Today, most users don't need to worry about IRQ settings because all devices are now plug and play, which means they are configured automatically. The following table is an overview of the traditional IBM IRQs, I/O ports, and their related devices.

IRQ Device I/O Port Bus slot Card type
00 System Timer None NO NONE
01 Keyboard None NO NONE
02 Cascade Controller
2nd PIC
03 COM 2 and 4 COM 2: 02F8h (02F8 or 2F8)
COM 4: 02E8h (02E8 or 2E8)
YES 8 or 16-BIT
04 COM 1 and 3 COM 1: 03F8h (03F8 or 3F8)
COM 3: 03E8h (03E8 or 3E8)
YES 8 or 16-BIT
05 Sound
Parallel port 2
Parallel port 2:
0278h - 0378h
YES 8 or 16-BIT
06 Floppy 03F0 - 03F5 YES 8 or 16-BIT
07 Parallel Port 1 0278h - 0378h YES 8 or 16-BIT
08 Real-time clock None NO NONE
09 Redirected IRQ 2
Network Available
None YES 8 or 16-BIT
10 Open None YES 8 or 16-BIT
11 Open
SCSI (small computer system interface)
YES 8 or 16-BIT
12 Open
None YES 8 or 16-BIT
13 Coprocessor None NO NONE
14 Open
Primary hard drive
Hard drive controller
1ST IDE: 1F0 YES 8 or 16-BIT
15 Open
2nd hard drive (secondary)
2ND IDE: 170 YES 8 or 16-BIT

Technically, there are 16 IRQs if you count IRQ 0. The system timer and all IRQs above 15 are known as virtual IRQs and handled by both the operating system and APIC (Advanced Programmable Interrupt Controller).

Computer acronyms, Device, DMA, Hardware conflict, Hardware terms, Interrupt handler, Interrupts, IRQL, Resource