IRQ12

IRQ12 is one of the standard interrupt request lines used in x86-compatible computer systems to signal the CPU from hardware devices. Interrupts are a mechanism that allows devices to request immediate attention from the processor, interruptting regular program flow for a short service routine. IRQ numbers are used by the system’s interrupt controller to identify the source of the interrupt.

Historically, IRQ12 has been most closely associated with the PS/2 mouse. On many older PCs and motherboards with a PS/2 port, the mouse commonly used IRQ12, while other devices occupied the remaining IRQ lines. With BIOS and operating system configurations that support legacy devices, IRQ assignments could be adjusted, but the PS/2 mouse frequently remained tied to IRQ12 in typical setups. As USB mice became prevalent, reliance on the PS/2 IRQ mapping diminished.

In modern systems, IRQ assignments are managed by the operating system and platform firmware (BIOS/UEFI) and can be dynamic, especially on boards with PCI/PCIe devices and Advanced Configuration and Power Interface (ACPI) interrupt routing. IRQ12 may be allocated to various devices, including PCI or PCIe components or shared among devices in capable systems. The exact usage of IRQ12 is therefore not fixed across all hardware and can vary by motherboard, firmware, and OS configuration. In virtualization environments, IRQ mappings can also differ from the host hardware.

Troubleshooting generally involves checking current interrupt assignments with the operating system tools: Linux users can view /proc/interrupts, while Windows users can inspect Device Manager or System Information for resource conflicts. If a PS/2 device is in use or a legacy PS/2 port is enabled, IRQ12 may be involved; otherwise, modern USB peripherals and dynamic routing may render the IRQ12 line reserved for other purposes.

See also: Interrupt request (IRQ), 8259 PIC, PS/2.