Units are needed to follow a protocol so that the interrupt-request (IRQ) strains is often shared. The PCI bus involves 4 interrupt traces, INTA# by means of INTD#, all of which are available to every product. Approximately 8 PCI units share the exact same IRQ line (INTINA# via INTINH#) in https://nathanlabsadvisory.com/sama-compliance-saudi-arabia/