Units are needed to observe a protocol so which the interrupt-ask for (IRQ) strains can be shared. The PCI bus involves 4 interrupt lines, INTA# by INTD#, all of which are offered to every device. As much as eight PCI devices share a similar IRQ line (INTINA# by INTINH#) in https://nathanlabsadvisory.com/certified-data-privacy-professional-cdpp/