System IRQ's

Discussion in 'Computer Information' started by Jerry G., Jul 31, 2004.

  1. Jerry G.

    Jerry G. Guest

    I am looking at my system in both system information, and in the computer

    I cannot see the following IRQ's: 3, 5, 7, 11, and 17. I am very
    curious to know why Windows did not assign them, and doubled up others to be

    The second thing is that I cannot seem to figure out what USB device is on
    what USB Universal Host Controller. Each controller has a set of ports in
    association with it. I found the Host Controller addresses.

    What I want to do in the end, is to determine exactly which USB device is in
    which port when viewing it in the System Hardware Properties.

    It turns out that one of the USB Host Controllers is being shared in IRQ
    with the ATA hard drive. Another Host Controller is being shared with a
    modem. There is another one that is being shared with the video display.

    I have an HP 4670 Scanner, and it is giving loss of communications problems
    because of the IRQ sharing. I found this out after doing a lot of searching.
    To get around that, I used the USB Host Controller that in shared with the
    least demand. This was the one that is shared with the modem. The scanner
    was now, only failing to communicate once in a while.

    To resolve the issue, I added an active USB hub to act as a type of buffer.
    It actually is slowing down the USB communications. With this approach, the
    scanner seems to be working for now. I tried it many times over the coarse
    of the evening, and it has not failed yet.

    What I am looking for, is if someone would have an explanation for this???
    Jerry G., Jul 31, 2004
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  2. Jerry G.

    Linda Guest

    15 is the highest IRQ number.
    Linda, Jul 31, 2004
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  3. Jerry G.

    Grinder Guest

    I won't pretend that I have a comprehensive view of this either. Here
    is some dated information, however, for what it's worth:
    Grinder, Jul 31, 2004
  4. Jerry G.

    DeMoN LaG Guest

    No, Windows 2000/XP can assign virtual IRQs. Example from the computer I'm
    in front of:

    IRQ 18 - ATI Capture Card
    IRQ 19 - GF4 Ti4400
    IRQ 20 - 2 10/100 NICs (a 3com and an nVidia), 2 nVidia audio devices, a
    firewire controller, 2 USB controllers, and the PCI to USB controller.

    There are only 15 /physical/ IRQs
    DeMoN LaG, Jul 31, 2004
  5. Jerry G.

    Chaos Master Guest

    Jerry G. caused an illegal operation in module
    Same problem here... my modem is sharing IRQ with nothing (it seems) but it
    still says the IRQ is shared!

    Check the BIOS to see if the IRQ setup is configured to be automatical, and if
    there's 'Assign IRQ for VGA' enabled. I've had similar problems with my modem
    (slow connection, blue screen)

    Chaos Master, Jul 31, 2004
  6. Jerry G.

    Michael-NC Guest

    This pertains more to win98 but may provide some help.

    There are 16 IRQs (15 usable) in a computer system. Here is a typical
    assignment of these IRQs:

    IRQ 0 System- System Timer
    IRQ 1 System- Keyboard
    IRQ 2 System- Cascadeable PIC (programmable interrupt controller), controls
    IRQ 8-15
    IRQ 3 System- Serial Port (COM 2 and COM4)
    IRQ 4 System - Serial Port (COM 1 and COM3)
    IRQ 5 Available- General Adapter Use
    IRQ 6 System- Diskette Controller
    IRQ 7 System- Printer 1
    IRQ 8 System- CMOS Real-time clock
    IRQ 9 Available- General Adapter Use
    IRQ 10 Available- General Adapter Use
    IRQ 11 Available- General Adapter Use
    IRQ 12 System- Mouse Port
    IRQ 13 System- Math Co-processor (even though this is built into the CPU, it
    still uses an IRQ)
    IRQ 14 System- Hard Disk Controller
    IRQ 15 Available- General Adapter Use

    As you can see, there are five (5) IRQs that are not assigned by the system
    design. Of these, one usually goes to the graphics card, one to the USB
    ports, and one to the modem. That leaves two (2) available IRQs for
    everything else. With care (and use of the proper cards), this is normally

    Loading Sequence for Additional cards:

    Internal Modem (PCI)
    Sound Card (PCI or ISA)
    Network Card, a.k.a. NIC (PCI or ISA)
    DVD Devices requiring Dxr3 Decoder Board (PCI)
    Note: Some video decoder boards require two (2) IRQs for complete
    functionality. Check with your video decoder card manufacturer for video
    decoder support and requirements.
    SCSI Adapter (PCI) (This assumes that the system does not have a SCSI hard
    Any others.
    Michael-NC, Jul 31, 2004
  7. Sub-text: "I won't reply anymore therefore I win."
    ~misfit~, the malicious, surnaming gonad, Aug 1, 2004
  8. Jerry G.

    DeMoN LaG Guest

    ACPI and APIC are two different things. Go ogle yourself.
    DeMoN LaG, Aug 1, 2004
  9. Jerry G.

    relic Guest

    There are 4 entries. NOTHING to do with System IRQ's is mentioned in them.
    That would be ACPI.
    relic, Aug 1, 2004
  10. Jerry G.

    Isoshi Guest

    In this threads context of additional IRQ's, and IRQ Steering, I'd agree
    with relic; it's ACPI.
    Isoshi, Aug 1, 2004
  11. Howdy!

    Four? I get 54,200 on "Advanced Programmable Interface Controller",
    including (as the FIRST hit) info on the Intel 82093AA. Info at .

    Try Googling with intelligent choices sometimes. Or better still,
    study some. You just might learn something.

    Ralph W. Phillips, Aug 2, 2004
  12. Jerry G.

    Wizard Guest

    not using XP.
    Wizard, Aug 2, 2004
  13. Jerry G.

    Diogenes Guest

    Diogenes, Aug 2, 2004
  14. Jerry G.

    JT Guest

    JT, Aug 2, 2004
  15. Jerry G.

    relic Guest

    I probably sounded like I'm trying to argue that it's /not/ APIC, it's that I
    saw advice to the OP about using APIC. I believe the option in BIOS is ACPI,
    not APIC; at least it is on the motherboards I've seen lately. You have to
    enable ACPI to get APIC.
    relic, Aug 2, 2004
  16. Jerry G.

    zink Guest

    So, what about the shared IRQ lines? Why doesn't the OS just assign
    each PCI object its *own* interrupt?
    zink, Aug 3, 2004
  17. Jerry G.

    Stuart Guest

    Stuart, Aug 3, 2004
  18. Jerry G.

    JT Guest

    Depends heavily on the BIOS and what they have modified. APIC does not Have
    to depend on ACPI.

    You came across as though APIC didn't exist, which it very much does. You
    also came across as though APIC didn't have anything to do with IRQs and
    sharing, which it very much does. You also said that there were only 4
    google results and they had nothing to do with IRQs. That was just wrong.

    JT, Aug 3, 2004
  19. Jerry G.

    relic Guest

    I said, "Advanced Programmable Interface Controller" didn't in the context of
    IRQs. It doesn't.
    That was confusing as I wrote it and I admitted to that already. The BIOS
    option the OP would most likely have seen was ACPI, not APIC.
    Here it is, *4* google results that have nothing to do with IRQs:
    Web Results 1 - 4 of 4 for "Advanced Programmable Interface Controller""&btnG=Google+Search

    As you can see, it was just _correct_
    relic, Aug 3, 2004
  20. The P4 technology machines have 24 IRQ's, while the P3 have 17 IRQ's.
    The new Athelon series type machines also have 24 IRQ's.

    Jerry G.
    Jerry Greenberg, Aug 4, 2004
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