What is an IRQ conflict?

When a device such as a keyboard or printer needs the attention of the CPU, it sends a signal via its assigned IRQ (interrupt request) line. When the CPU detects the interrupt, it knows which device is signaling and allocates its time based on the requester�s priority. Some IRQs are permanently assigned (e.g., the keyboard is always IRQ 1). However, other IRQs can be assigned by the user.

Generally only one device can be assigned to a specific IRQ line. If two devices are inadvertently assigned to the same IRQ, the CPU cannot distinguish which device is signaling and the result is an IRQ Conflict.

Two devices can share the same IRQ; they just can�t use it at the same time. For example, if both the mouse and a modem are assigned to IRQ 3 (COM2), a conflict could develop. Typically one or both of the devices will lock up or start behaving erratically. It is possible for an IRQ conflict to render the entire system inoperable.