Units are necessary to observe a protocol so that the interrupt-request (IRQ) strains can be shared. The PCI bus contains four interrupt strains, INTA# by INTD#, all of which can be obtained to each unit. As much as eight PCI equipment share the same IRQ line (INTINA# through INTINH#) in https://nathanlabsadvisory.com/adgm-data-protection-regulation-compliance/