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How To Find Irq Assignments

Most components directly attached to your motherboard—including PCI slots, IDE controllers, serial ports, the keyboard port, and even your motherboard’s CMOS—have individual interrupt requests (IRQs) assigned to them.

An interrupt request line, or IRQ, is a numbered hardware line over which a device can interrupt the normal flow of data to the processor, allowing the device to function.

Windows Vista and 7 lets you prioritize one or more IRQs (which translate to one or more hardware devices), potentially improving the performance of those devices.  Below are basic registry editing tips that you can use to set IRQ priorities.

1. Start by opening the System Information utility (msinfo32.exe), and navigating to System Summary\Hardware Resources\IRQs to view the IRQs in use on your system, and the devices using them.

Take note of IRQ13 (Numeric Data processor) that we will use in this example:


2. Next, open the Registry Editor and navigate to the following key. If PriorityControl doesn’t exist, create the key under Control.

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\PriorityControl


3. Create a new DWORD value in this key, and call it IRQ#Priority, where # is the IRQ of the device you wish to prioritize (e.g., IRQ13Priority for IRQ 13, which is your numeric processor).


4. Double-click the new value, and enter a number for its priority. Enter 1 for top priority, 2 for second, and so on. Make sure not to enter the same priority number for two entries, and keep it simple by experimenting with only one or two values at first.


5. Close the Registry Editor and reboot your computer when you’re done.

Some users have gotten good results prioritizing IRQ 8 (for the system CMOS) and the IRQ corresponding to the video card, but the feedback is unconfirmed. Do you think it is a placebo tweak? Post your comments!

An IRQ (Interrupt Request) number is assigned to all the hardware devices installed in a computer that are used to input information, for example the mouse or the keyboard. On a PC, some IRQs are predefined, so the Keyboard controller is always given an IRQ of 1, for example. IRQs 5, 7, 9, 10, 11, and 12 are usually left available for add-on devices. In modern computers, IRQs are usually assigned dynamically and it is rare to see an IRQ conflict. If two devices on the computer do have the same IRQ number assigned to them, the IRQ conflict will cause one or both of them to fail. You can troubleshoot IRQ issues from Device Manager in computers running Windows.

Video of the Day

Devices in a computer use IRQs to gain access to the CPU

Step

Click "Start," then click "Control Panel" to open the Control Panel window. Double-click the "System" icon to open the "System Properties" window.

Step

Click the "Hardware" tab, then click the "Device Manager" button. This opens the Device Manager.

Step

Click the "View" menu at the top of the Device Manager window. Select "Resources by type" from the drop-down list. This displays a list of resource types.

Step

Click the expansion box next to the "Interrupt request (IRQ)" icon. This displays a list of system devices and the IRQ numbers assigned to them. Devices with conflicting IRQs will be identified by an exclamation mark inside a yellow circle. Make a note of the IRQ number issued to the conflicting devices.

Step

Right-click each conflicting device and select "Properties." In the Properties window for each device, click the "Resources" tab. Check to see if the conflicting devices have reserved IRQs. If the option to change resource settings is unavailable (greyed-out) you can not reassign IRQs from within Device Manager because the IRQs are resereved. If the option to change the IRQ resource setting is available, you will be able to assign a new IRQ if one is available. Close all open windows.

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