What interrupt request is redirected to IRQ 9?

In many systems, the interrupt request (IRQ) that is redirected to IRQ 9 is typically used for the ACPI (Advanced Configuration and Power Interface) or for certain legacy devices, such as the interrupt for the integrated interrupt controller. Additionally, IRQ 9 can also be associated with the system timer in some architectures. The exact usage can vary based on the hardware and operating system configuration.