Units Are necessary to adhere to a protocol so the interrupt-request (IRQ) traces might be shared. The PCI bus consists of 4 interrupt traces, INTA# through INTD#, all of which are available to every device. As many as 8 PCI gadgets share the exact same IRQ line (INTINA# through INTINH#) https://nathanlabsadvisory.com/nydfs-cybersecurity-risk-assessment/