Units are necessary to comply with a protocol so the interrupt-ask for (IRQ) strains is usually shared. The PCI bus features four interrupt lines, INTA# through INTD#, all of which are available to each product. Approximately eight PCI products share the same IRQ line (INTINA# by INTINH#) in APIC-enabled x86 https://nathanlabsadvisory.com/finra/