Units are needed to stick to a protocol so the interrupt-ask for (IRQ) strains may be shared. The PCI bus features 4 interrupt traces, INTA# by means of INTD#, all of which are offered to each machine. Nearly eight PCI products share precisely the same IRQ line (INTINA# through INTINH#) https://nathanlabsadvisory.com/beta-testing-software-applocation/