How do I assign the correct IRQs?

Okay, I've already built my system. It's been running for about a month now. But, I think I have some PCI cards sharing IRQs. I've looked at the motherboard manual, but I'm not sure what it means, especially the ones with "INT-A" and "INT-B"...etc. Can someone explain to me how this works? I don't mind a lot of detail because I really want to learn as much as I can.

System Specs:
Asus A7V133 (no audio)
Athlon Thunderbird 850
<A HREF="" target="_new">256MB SDRAM PC133, unbuffered, CL=2</A>
IBM DTLA-307030, Ultra ATA100, 30GB, 7200RPM
Creative Soundblaster Live!
3Com 3C905B-TX-NM Fast Etherlink XL 10/100 TX NIC
Teac 3.5" Floppy Disk Drive
Swiftech MC370-0A


<i>OC...unless your computer's cheezy (is that a good rhyme?)</i> :eek:
5 answers Last reply
More about assign correct irqs
  1. If you don't understand what the manual is babbling about, then use trial and error method. Heres a rough guide. First without changing anything take note what irq is assigned to what peripheral when your system boot-up. If its too fast to read, press PAUSE so that it will freeze. Then try changing the INT-A,B,C or D, one at a time and see what peripheral is affected by the change. This way, you will know which pci slot correspond to which INT in the bios.

    Happy trying.
  2. Unless you experience problems (freezing, sound glitches etc...) you dont need to reserve uniques IRQ's for your PCI card. However, to check for IRQ's sharings, use the system information tool (I think it comes with either Win98+ and MS Office, but I'm not sure). If you have two PCI/AGP cards sharing an IRQ, you can assign a different IRQ in BIOS or simply change your problematic PCI card to another slot.

    Hope that helps.

    It's better to be rich and healthy than poor and sick!
  3. try a tool like sisoft's sandra.

    there are only two types of class. first and none
  4. The INT-A through D refer to hardware interrupts. These are the real interrupt lines and there are fewer of them than the number of PCI slots and/or devices on your machine. IRQs are software interrupt vectors. PCI allows sharing of IRQs, the hardware allows sharing of hardware interrupts, too. Obviously you will get a cleaner separation of devices if the hardware interrupts are not shared. Take a look at for info on these interrupts and typical uses for the PCI slots. This is mainly FYI, I tend to agree with the poster who said "if it ain't broke, don't fix it".

    I should mention given your combination of parts, assuming you have your disk(s) on the primary/secondary IDE controller(s) and are not using the Promise controller, I would configure it as follows:
    Radeon card in AGP slot, slot 1 left blank
    3COM card in slot 2
    SB Live in slot 3
    Disable COM2 in BIOS; optionally disable COM1 also
    Assign IRQ11 to slot 1 (goes to Radeon card)
    Assign IRQ10 to slot 2 (goes to 3COM card)
    Assign IRQ5 to slot 3 (goes to sound card)
    Assign IRQ3 to slot 4/5 (goes to USB because they're blank)
    Optional: Use IRQ4 for the sound card, and "reserve IRQ5 for legacy device" in BIOS to allow SB emulator to have it.
    <P ID="edit"><FONT SIZE=-1><EM>Edited by dmcmahon on 05/12/01 09:52 AM.</EM></FONT></P>
  5. Sharing or conflicting? If you see "?" and "!" marks on windows, or some devices does not work they are conflicting (that is unusual on PCI). If not that means that you have no problem, PCI cards supose to share IRQs . It all happen automaticly by os. (I heard that new windoze puts ALL devices in one IRQ, and that is too much and could be a problem). INT-A-B-C-D is interrupt lines inside PCI bus that translated into IRQs when they go out of pci bus. Because of that translation it is possible for few devices to use the same IRQ. IRQs is interupt lines that conected to PIC (deep inside chipset), which is connected to cpu . IRQ are NOT software vectors.
    You should configure devices to "autodetect" ,unless there is a problem.

    -Beer! Good!
    -James Hatefild
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