IRQ stands for Interrupt ReQuest and refers to special
numbered channels that are used by devices to get the processors
attention.
For example, when you press a key on your keyboard this sends a signal to
the processor via an IRQ channel (usually IRQ 1) to let it know that it
needs to process some data.
IRQ conflicts can occur when new hardware is installed or reconfigured, for
example, it can cause problems if you have your mouse on COM 1 (IRQ4) and a
modem on COM 3 (IRQ4), below is a list of the default assignments for IRQ
channels in Windows XP.
Default ISA IRQ Assignments
IRQ 0
System Timer
IRQ 1
Keyboard
IRQ 2
Cascaded with IRQ 9
IRQ 3
Default COM2 and COM4
IRQ 4
Default COM1 and COM3
IRQ 5
LPT2
IRQ 6
Floppy Drive Controller
IRQ 7
LPT1
IRQ 8
Real Time Clock
IRQ 9
SEE 2
IRQ 10
Open
IRQ 11
Open
IRQ 12
PS/2 mouse or Open
IRQ 13
Math Coprocessor
IRQ 14
Primary Hard Drive controller
IRQ 15
Secondary Hard Drive
controller
Viewing your current IRQ assignments
To view your current IRQ assignments you can
open Device Manager.
Click on START, click on CONTROL
PANEL.
Click on Performance and Maintenance.
Click on System.
Click on the Hardware tab.
Click the DEVICE MANAGER button.
Once you have Device Manager open,
select VIEW from the toolbar menu and then click Resources by Type.
Double click on Interrupt Request (IRQ) as seen in fig 1.1 below:
The list that appears on your machine will vary depending on the hardware you
have.
If you are experiencing problems with a newly installed/configured piece of
hardware and the drivers are installed correctly then check to see if it has its
own IRQ channel.
Changing IRQ Settings
Warning: Changing system resources such
as IRQ channels can result in your computer not functioning correctly, always
make a note of the settings before you change anything so you can restore them
back if required.
If you do have a conflict and need to change an
IRQ setting:
Right click on the device in the list (see
above) and then select properties.
Click the Resources tab.
Remove the tick from the Use automatic
settings option.
Select a non-conflicting configuration from
the pull down box.
Click OK
You may find you cannot manually change your
IRQ settings (the Use automatic settings will be greyed out), this is
usually related to the ACPI function used by Win XP.
To resolve conflicts with PCI or ISA cards try manually setting them in your
motherboard's BIOS or try a different slot for the newly installed device, you
will usually find that by changing the slot you will change the IRQ channel as
well.
