IRQ

Bus Line?

Priority

Typical Default Use

Other Common Uses

0

no

1

System timer

None

1

no

2

Keyboard controller

None

2

no (rerouted)

n/a

None; cascade for IRQs 8-15. Replaced by IRQ 9

Modems, very old (EGA) video cards, COM3 (third serial port), COM4 (fourth serial port)

3

8/16-bit

11

COM2 (second serial port)

COM4 (fourth serial port), modems, sound cards, network cards, tape accelerator cards

4

8/16-bit

12

COM1 (first serial port)

COM3 (third serial port), modems, sound cards, network cards, tape accelerator cards

5

8/16-bit

13

Sound card

LPT2 (second parallel port), LPT3 (third parallel port), COM3 (third serial port), COM4 (fourth serial port), modems, network cards, tape accelerator cards, hard disk controller on old PC/XT

6

8/16-bit

14

Floppy disk controller

Tape accelerator cards

7

8/16-bit

15

LPT1 (first parallel port)

LPT2 (second parallel port), COM3 (third serial port), COM4 (fourth serial port), modems, sound cards, network cards, tape accelerator cards

8

no

3

Real-time clock

None

9

16-bit only

4

Network cards, sound cards, SCSI host adapters, PCI devices, rerouted IRQ2 devices

10

16-bit only

5

Network cards, sound cards, SCSI host adapters, secondary IDE channel, quaternary IDE channel, PCI devices

11

16-bit only

6

Network cards, sound cards, SCSI host adapters, VGA video cards, tertiary IDE channel, quaternary IDE channel, PCI devices

12

16-bit only

7

PS/2 mouse

Network cards, sound cards, SCSI host adapters, VGA video cards, tertiary IDE channel, PCI devices

13

no

8

Floating Point Unit (FPU / NPU / Math Coprocessor)

None

14

16-bit only

9

Primary IDE channel

SCSI host adapters

15

16-bit only

10

Secondary IDE channel

Network cards, SCSI host adapters