Units are necessary to follow a protocol so which the interrupt-request (IRQ) strains is often shared. The PCI bus features four interrupt traces, INTA# via INTD#, all of which can be found to each product. Around eight PCI equipment share a similar IRQ line (INTINA# through INTINH#) in APIC-enabled x86 https://nathanlabsadvisory.com/spear-phising/