Why are all my devices using one IRQ in Win2K or WinXP?

Updated 05/09/2007 04:30 PM

Why are all my devices using one IRQ in Win2K or WinXP?

Windows 2000 or Windows XP has been installed in ACPI mode and that is how it assigns its plug and play resources. This is normal.  While most people experience no problems, other people can encounter some problems. Usually it's all assigned to IRQ9, sometimes IRQ11.  In theory,  this single IRQ is used as a gateway to 255 virtual IRQs above 15.  By allowing Windows 2000 to automatically assign your resources, you will not have to juggle IRQ assignments, which lets you install more devices that require IRQs than before. Windows 2000 uses ACPI to manage Plug and Play, device enumeration, the dynamic loading and unloading of drivers, and system power management. In addition, if your motherboard's chipset and BIOS fully support an IO-APIC, the ACPI HAL will allow the system to take advantage of hardware IRQs available above 15. This is especially important on dual processor systems.

These are not conflicts: this is IRQ sharing.  Most PCI devices, along with AGP video cards, are designed to accommodate and support IRQ sharing.

If you have no problems, it is highly recommended that you leave the assignments alone.

Usually problems with systems installed in ACPI mode can be attributed to hardware, BIOSes, firmware and/or drivers that are not fully ACPI  compliant.  To avoid problems, you should always use the latest BIOSes, firmware and drivers wherever possible.

Please review your motherboard's PCI Interrupt Request Routing (IRQ) table for card placement.  IRQ are hardware lines over which devices can send signals to the CPU.  This will tell you which slots on your motherboard are shared.

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