Equipment are needed to observe a protocol so that the interrupt-ask for (IRQ) traces may be shared. The PCI bus contains 4 interrupt traces, INTA# via INTD#, all of which are available to each system. Around 8 PCI products share precisely the same IRQ line (INTINA# by means of INTINH#) https://nathanlabsadvisory.com/rbi-cyber-security-framework/