Equipment are required to follow a protocol so the interrupt-ask for (IRQ) lines is often shared. The PCI bus includes four interrupt strains, INTA# through INTD#, all of which are offered to every unit. Nearly eight PCI products share exactly the same IRQ line (INTINA# by INTINH#) in APIC-enabled x86 https://nathanlabsadvisory.com/soc-2/