Products Are required to observe a protocol so that the interrupt-request (IRQ) strains may be shared. The PCI bus consists of 4 interrupt lines, INTA# by INTD#, all of which are available to each device. As many as eight PCI products share the exact same IRQ line (INTINA# through INTINH#) https://nathanlabsadvisory.com/iso-22301-business-continuity/