IRQ 
interrupt request 
In PCs, an IRQ is a signal from a peripheral device indicating that it needs the CPU to do something. For example, the graphics adapter may request permission to refresh the screen. The interrupt request signals run along the IRQ lines to an interrupt controller that assigns priorities to incoming IRQs and delivers them to the CPU. To avoid conflicts, a unique value must be specified for each device and its path. Before Plug and Play became popular, users often had to set IRQ values manually when installing new peripherals.