Devices are necessary to comply with a protocol so that the interrupt-ask for (IRQ) traces could be shared. The PCI bus contains 4 interrupt strains, INTA# by way of INTD#, all of which are available to each machine. Approximately 8 PCI devices share a similar IRQ line (INTINA# via INTINH#) https://nathanlabsadvisory.com/mobile-app-development/