IRQ (Interrupt ReQuest)

A hardware interrupt on a PC. There are 16 IRQ lines used to signal the CPU that a peripheral event has started or terminated. Except for PCI devices, two devices cannot use the same line. If a new expansion card is preset to the IRQ used by an existing card, one of them must be changed, especially under 95/98/ME. Windows 2000/XP rarely has this problem, but then some motherboards seem to be fussy and will need help in this department even with Windows 2000/XP.

How to check the IRQ assignment (for NT/2000/XP see below):

1. Go to Start/Settings/Control Panel.

2. Double-click on System

3. Select the Device Manager tab.

4. Double-click on Computer. It is the top entry in Device Manager.

5. The next screen lists all of the devices and the IRQ assigned for that device. The list is in numerical order and starts with 00 and ends with 15.

An IRQ is considered available if it meet one of two criteria:

A. If a number is not listed at all, then it is available or

B. If a number is listed only once and the device assigned to it is "IRQ Holder for PCI steering", then it is available.

If you do NOT have an available IRQ you should reconfigure your system to free one up. We have some suggestions on how to accomplish this.

How to free up an IRQ:

There are many ways to free up IRQ's, some are easier than others, some cost money. Below is some general advice on freeing up IRQ's. Performing the steps below may require the assistance of the vendor of the device that you are trying to configure (i.e. motherboard, computer, sound card, etc.)

1. First you have to realize that the "IRQ Holder for PCI steering" is not a device. Any IRQ that is assigned to JUST the "IRQ Holder for PCI steering" is an available IRQ.

2. Disable any unused devices. Many users do not use devices such as the USB port (universal serial bus), 2nd IDE port, IDE port on a sound card, etc. The USB and 2nd IDE port are usually devices that are on the motherboard and can be disabled in the motherboard BIOS. Call your sound card vendor if it has an IDE port on it that is not disabled. If you have a modem, 2nd serial port or any other device that you are not using, it could also be disabled to free up resources.

3. Reconfigure your sound card to use less resources if it is using 2 or more IRQ's. In Device Manager, go to Sound, Video and Game Controllers. Find your sound card driver and double-click on it. Select the Resources tab. Uncheck the box marked "Automatic Settings". The "Settings based on" will then activate and you can choose a different configuration such as Basic configuration 0001, 0002, etc. Contact your sound card vendor if you require assistance.

4. If your graphics card is assigned an IRQ, see if your motherboard BIOS supports turning off the IRQ assigned to it. If it does, turn off the IRQ assignment. Not all motherboards support this. Please contact your motherboard or computer vendor for assistance with this.

5. If you have an unused com port and are using a PS/2 mouse, connect a serial mouse and disconnect the PS/2 mouse. Then disable the PS/2 mouse in the motherboard BIOS. Please contact your motherboard or computer vendor for assistance with this.

6. If disabling doesn't work, try reserving an already used IRQ instead. This will force the system to reassign everything.

7. Switch boards in the PCI slots. The IRQ is often connected to one slot.

8. Most BIOSes have a menu for IRQ assigment. Here are some generic tips:

• Set the PnP OS Installed parameter (if available) to NO and the Reset Configuration Data

parameter (if available) to YES.

• Switch to manual configuration mode (if applicable) and set one of the IRQs that you want to

reserve for a card to Legacy ISA/non-PnP mode. Save changes in CMOS settings.

• Turn your system off and take the card out.

• Turn the system on and load Windows 95/98. Check with its Device Manager if IRQ assignments

have become "less crowded" and the IRQ number that you just reserved is not shown among the

occupied ones.

• Shutdown and turn off the system again and put the card back.

• Go to the BIOS CMOS Setup program and switch the reserved IRQ line back to the PCI/PnP mode

before loading Windows 95/98. The device should now take that IRQ line exclusively. If it did not, remove the card line

using the Device Manager and restart Windows.

In Windows NT:

It is important to realize that there is no way to change IRQ assignments for PCI cards in Windows NT.

This can be done only by using the PCI/PnP configuration or similar menu in BIOS CMOS Setup

program invoked at the boot time.

It will definitely help if you disable some of the integrated PC peripherals from the Integrated

Peripherals or similar menu in the BIOS CMOS Setup program. In particular, try disabling one or more

Serial (COM) or Printer (LPT) ports. You may also disable the USB and/or the Secondary IDE

controller if needed. To achieve the maximum effect, try setting the PnP OS Installed parameter (if

available) to NO (since Windows NT 4.0 is not a Plug-and-Play operating system!). Also, switch the

Reset Configuration Data parameter (if available) to YES.

In Windows 2000/XP:

In Windows 2000/XP, some or all of the devices on your ACPI motherboard may be listed on the Resources tab in Device Manager as using the same IRQ. You cannot change the IRQ setting because the setting is unavailable. This occurs because Windows 2000/XP takes advantage of the ACPI features of the motherboard, including advanced PCI sharing. This feature lets you add more devices without generating IRQ conflicts.

If you need to manually assign IRQ addresses through the BIOS to a device on an ACPI motherboard, you'll have reinstall Windows as an upgrade after disabling the ACPI (Usually found under "Power management" in the BIOS menu). Follow these steps:

• Boot to BIOS

• Disable PnP OS

• Disable BIOS control of Power Management

• Install Windows 2000 from cd or boot disks

At the very start of the installation (blue screen) Windows tells you to press F6 if you want to install a third party SCSI or RAID driver. At this point, press F7. Nothing visible happens, but this will tell the computer that you don't want an ACPI installation. Just go on. If Windows refuses to do an upgrade and insists on a new installation, choose Automatic Repair.