IRQ (Interrupt Request)
An interrupt request (IRQ) is a hardware signal sent to the processor instructing it to suspend its current activity and handle some external event, such as a keyboard input or a mouse movement. In x86 based computer systems, IRQs are numbered from 0 to 15. Newer computers, including x86-64 systems, provide more than these 16 interrupts (usually 24). Some interrupts are reserved for specific purposes, such as the keyboard and the real-time clock; others have common uses but may be reassigned; and some are left available for extra devices that may be added to the system.
Here is a list of the IRQs and their common purposes in the x86 system:
In Linux, IRQ mappings are stored in the /proc/interrupts file:
In the picture above, you can see the names of the drivers that are using each IRQ. For example, the floppy driver is using IRQ 6.