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How to Disable PCI Bus IRQ Steering in Windows
Article ID: 182628 - View products that this article applies to.
This article was previously published under Q182628
If this article does not describe your hardware-related issue, please see the following Microsoft Web site to view more articles about hardware:
To disable PCI bus IRQ steering, follow these steps:
The following settings determine which routing tables Windows uses when programming IRQ steering:
For additional information about PCI bus IRQ steering, click the article number below to view the article in the Microsoft Knowledge Base:
(http://support.microsoft.com/kb/182604/EN-US/ )Description of PCI Bus IRQ Steering
The PCI local bus has become the industry-standard bus and is used in most Pentium-based computers. When a computer with a PCI local bus starts, the system BIOS dynamically configures all the PCI adapter resource settings and requirements because the PCI bus and PCI devices use agreed-upon mechanisms for identifying themselves and declaring their resource settings and requirements.
PCI devices can share the same IRQs because the system BIOS builds a table that is called the PCI IRQ routing table. This table includes entries for each PCI device that is given an ISA IRQ that is mapped to a particular PCI INT number that is associated with the specific PCI slot in which the device is installed. These are combined to create a link value. The link value is used when communicating with the device, and although PCI devices may use the same IRQ, they all have individual link values.
After the system BIOS assigns resource settings and builds the PCI IRQ routing table, Windows loads and extracts the PCI and ISA Plug and Play-compliant device resource information from the system BIOS and reads the information from the PCI IRQ routing table. Windows can reassign the ISA IRQs that are mapped to a particular PCI INT number. Windows can also dynamically reassign the IRQs when a Plug and Play event occurs, such as docking a laptop with its docking station.
Sometimes when is is reassigning IRQs in this way, Windows may hang, reboot, or have a device not work when it tries to reassign the IRQs that are set up by the BIOS. You can prevent Windows from dynamically allocating ISA interrupts by turning off IRQ steering. This prevents Windows from dynamically allocating interrupts, and relies on your system BIOS to do so.
Original Equipment Manufacturers (OEMs) may find it necessary to disable IRQ steering even on new PCs to prevent hardware resource conflicts on devices they have installed. This does not cause any loss of functionality for the devices, it simply ensures that the devices will remain enabled to use a specific IRQ configuration that the OEM has found to work properly when testing the system.
Article ID: 182628 - Last Review: January 22, 2007 - Revision: 3.1