Solving IRQ Conflicts

August 30, 1999

Debera White wrote:

Q.I have a network adapter I am trying to add to my system (amd-k6/400mhz with 64 mb,32x cd-rom 56k.v90 IBM Aptiva).  The problem is every time I try to use it it shows a conflict.  A friend of mine who recently moved out of state made the comment "why don't you just add another irq to your system"?.   My question is this "How do you do that?".  Can you help me or suggest something else?

Eric Georgieff answered:

A.Possible Solution:

I will take for granted that you are using Windows 95 or 98, since the situation may be different for Windows NT.

It helps to understand how IRQ's work, when trying to solve the many conflicts they can cause. Quite simply, all hardware devices connected to your system must use some of your Central Processing Unit's (CPU, or Processor's) processing power in order to operate and do something useful for you. When the hardware device needs your computer's CPU to accomplish such a task, it sends a message to the CPU telling it that it needs it's attention. This is called sending an Interrupt Request (IRQ). When the processor receives such a signal (an Interrupt Request), it remembers that the device in question needs it's attention (that it wishes to interrupt whatever it is currently doing), and proceeds to doing so only when it is finished taking care of the other system devices that are also requesting it's attention at the same time. Of course all this happens so fast that you probably will never notice that one device is requesting the CPU's attention and waiting to get it.

Alright, so all this seems simple enough, right? The thing is that each device can only send an Interrupt Request (IRQ) to the system processor using an assigned IRQ line. Furthermore, no two devices may be assigned to the same IRQ line. The problem arises when you consider that all modern IBM PC's or compatibles, have only 16 such IRQ lines (they are numbered 1 through 16) (much older computer might only have 8 IRQ'S), and you might sometimes want to have more then 16 devices connected to your system, without having a conflict. Also, some devices will only
work with certain IRQ lines, adding more to the problem.

You might have already come to the conclusion that since all computers have only 16 IRQ's (or sometimes 8), it is certainly impossible to "add another IRQ" as suggested your friend.

The solution however, is to reorganise what IRQ's your current devices use, in an effort to clear up the IRQ your network adapter wants to use. The way to do this is by going in the Windows Control Panel (Start > Settings > Control Panels), and choosing the System Panel. Then, switch to the Device Manager Tab (I guess this is where you found out that there was a conflict). Click on the device that is conflicting (there should be a yellow exclamation mark beside the conflicting device) and then click on the Properties button. Then go to the Resources tab and uncheck "Use Automatic Settings". You will then be able to change the IRQ of the selected device (by Clicking on "Interrup
Request" and then "Change Setting..."). Be patient and experimental.   If you can't find another free suitable IRQ for the network card, try changing that of other devices, in an effort to clear up the proper one required by your network card. Common devices that also use IRQ lines range from the Serial Ports on your computer to the Sound Card.  Remember to copy down the IRQ number that the device is currently using before changing it, in case the device won't work with the newly assigned IRQ line. You might also want to try the "Add New Hardware" wizard (also located in the Control Panels), if you haven't already done so. You could also try using the Conflicting Devices Windows Troubleshooter, although I doubt it would be of much use.

I know all of this sounds complicated, but don't worry it really isin't (especially if you've been adding Network Cards to your computer).