Units are needed to comply with a protocol so the interrupt-request (IRQ) lines could be shared. The PCI bus involves 4 interrupt lines, INTA# by means of INTD#, all of which are offered to every gadget. Around 8 PCI products share precisely the same IRQ line (INTINA# via INTINH#) in https://nathanlabsadvisory.com/cyber-security-policy-review/