There are several techniques to identify the requesting I/O module. These techniques also provide a way of assigning priorities when more than one device is requesting interrupt service.

With multiple lines, the processor just picks the interrupt line with highest priority. During the processor design phase itself priorities may be assigned to each interrupt lines.

With software polling, the order in which modules are polled determines their priority.

In case of daisy chain configuration, the priority of a module is determined by the position of the module in the daisy chain. The module nearer to the processor in the chain has got higher priority, because this is the first module to receive the acknowledge signal that is generated by the processor.

In case of bus arbitration method, more than one module may need control of the bus. Since only one module at a time can successfully transmit over the bus, some method of arbitration is needed. The various methods can be classified into two group – centralized and distributed.