Units are needed to observe a protocol so which the interrupt-request (IRQ) lines might be shared. The PCI bus incorporates 4 interrupt strains, INTA# through INTD#, all of which are available to every product. As many as 8 PCI gadgets share the same IRQ line (INTINA# via INTINH#) in APIC-enabled https://nathanlabsadvisory.com/supply-chain-security/