interrupt request (IRQ)
The Interrupt Request (IRQ) is a signal that informs the central processing unit( CPU) about a change in the computing process. If a hardware component in a personal computer( PC) requires the computing power of the central processing unit (CPU), it requests this power via an IRQ.
When an IRQ signal is triggered, the central processing unit (CPU) interrupts all current processes, saves the calculation status, branches to the corresponding routine, processes it and returns to the previously interrupted process. The IRQs are transmitted on specially provided data lines. The control is taken over by the interrupt controller, which evaluates and triggers the IRQs according to their priorities. The priority assignment allows an orderly control considering the preferred devices. If two plug-in cards send an interrupt request at the same time, then the IRQ with the higher priority is processed first.
The IRQs are marked with the digits 00 to 15, so that the CPU can recognize the triggering component by means of the IRQ. The upper IRQs from 8 to 15 can only be addressed by 16 bit signals and thus only via the ISA bus or the PCI bus.
The hardware interrupts are partly permanently assigned and can be triggered by the internal timer, the keyboard, the hard disk controller, the COM ports and the LPT interface, by sound cards, the USB controller or by interface signals.