Units are necessary to stick to a protocol so the interrupt-request (IRQ) traces is often shared. The PCI bus consists of 4 interrupt traces, INTA# as a result of INTD#, all of which are offered to every machine. Up to 8 PCI equipment share the same IRQ line (INTINA# via https://nathanlabsadvisory.com/data-protection-officer-service-virtual-dpo/