Equipment are required to stick to a protocol so the interrupt-request (IRQ) traces could be shared. The PCI bus contains four interrupt strains, INTA# through INTD#, all of which can be found to each system. Up to eight PCI equipment share the same IRQ line (INTINA# through INTINH#) in APIC-enabled https://nathanlabsadvisory.com/irs-efile-2/