What are the IRQ's used for?

IRQ Level

Common Use

Comments

0

Timer

Hard-wired on motherboard

1

Keyboard

Hard-wired on motherboard

2

Cascade from IRQ 9

May be available depending on Motherboard

3

COM2 or COM4

4

COM1 or COM3

5

LPT2

This is usually free as not many people have 2 parallel ports. Sound blaster cards usually use this.

6

Floppy disk controller

7

LPT1

Sound blaster cards can use this

8

Real-time clock

Hard-wired on motherboard

9

Cascade to IRQ 2

Wired directly to 2, sometimes tell software 9 when mean 2

10

Unused

This is usually used by Network cards, many of them not allowing it to be changed

11

Unused

Usually used by SCSI controllers

12

PS/2, Bus mouse

If you are not using a PS/2 or bus mouse this can usually be used by another device

13

Math Coprocessor

Used to signal errors

14

Hard disk controller

If you are not using an IDE hard disk you may use this for another device

15

Some computers use this for the secondary IDE controller

If you do not use the secondary IDE controller you may use this for another device