What is IRQ sharing?

[lost-and-found]

Supposedly some mobos have two PCI slots that have "IRQ sharing" what is it and how can I break it

I noticed that if I put two Cards, like sound and ethernet into the two slots that have IRQs shared I get weirdo Windows messages and stuff's not working, etc.

[John Prophet]

http://www.homenethelp.com/web/howto/irq-sharing.asp

evidently ethernet nics are pretty picky about sharing.

And I remember, even recently, having issues with sound cards and nics conflicting. The one was a problem with onboard sound on a biostar motherboard. I put a nic in and the nic would hang on install. Hmmm. Tried another NIC (same exact model). Same thing. I found out it was trying to share the IRQ with the onboard sound.

Hmm. So I disabled the sound in bios...and the nic installed and worked perfectly.

So I THEN re-enabled the sound..which I figured would then choose a different IRQ..but it just picked the same IRQ as before..the same as the NIC..but this time it worked fine. Go figure.

But yes, different motherboards have different rules for the way the different slots share IRQs. I only know certain rules of thumb such as trying to not use the slot next to the agp slot.

And of course in the old days many board had the shared PCI/ISA slot which obviously was an either/or sort of thing.

There are a million and one articles online about IRQs, sharing etc.

Here is one of the first things that google popped up. An old article and chart about the 440lx chipset and irq issues http://www.intel.com/support/motherb...440lx/irqs.htm

JP

[John Prophet]

And http://www.buildorbuy.org/irqmap.html

and this one is talking more of the aspect of the individual motherboard peculiarities http://techrepublic.com.com/5100-6255-5035033.html

And also...some cards have more leeway on which irqs they can use..whereas some cards have their heart set on one certain irq. Usually not an issue but if you get two cards determined to have a certain irq I guess it could be a problem.

Also W98ish comps and the W2k type handle the whole irq issue a little differently as several of the articles outline.

JP