Equipment are required to observe a protocol so the interrupt-request (IRQ) strains is often shared. The PCI bus consists of 4 interrupt strains, INTA# via INTD#, all of which can be obtained to every unit. Nearly eight PCI units share the same IRQ line (INTINA# by INTINH#) in APIC-enabled x86 https://nathanlabsadvisory.com/difc-data-protection-compliance/