Gadgets are needed to stick to a protocol so the interrupt-request (IRQ) lines could be shared. The PCI bus contains four interrupt lines, INTA# by means of INTD#, all of which can be obtained to each system. Nearly 8 PCI units share precisely the same IRQ line (INTINA# by INTINH#) https://nathanlabsadvisory.com/ciso-services-virtual-ciso/