Devices Are necessary to follow a protocol so which the interrupt-ask for (IRQ) lines could be shared. The PCI bus incorporates four interrupt lines, INTA# through INTD#, all of which are available to each system. As many as eight PCI equipment share exactly the same IRQ line (INTINA# through INTINH#) https://nathanlabsadvisory.com/ce-marking-services-european-notified-body/