Equipment are required to observe a protocol so that the interrupt-request (IRQ) lines might be shared. The PCI bus contains 4 interrupt lines, INTA# by way of INTD#, all of which can be found to every unit. Around eight PCI gadgets share precisely the same IRQ line (INTINA# by INTINH#) https://nathanlabsadvisory.com/cybersecurity-technical-writing/