Devices Are required to follow a protocol so the interrupt-request (IRQ) lines may be shared. The PCI bus includes four interrupt lines, INTA# via INTD#, all of which can be obtained to every device. Approximately eight PCI units share the identical IRQ line (INTINA# via INTINH#) in APIC-enabled x86 units. https://nathanlabsadvisory.com/ce-marking-services-european-notified-body/