With n-bit numbers, the comparator compares each digit of the number with an XNOR gate. Two n-bit numbers are only identical if each digit is identical. This results in the circuit diagram shown.
Identity comparators are used in computer communications. If the computer wants to communicate with its hard disk, it sends a number or address. The hard drive compares this address with a stored address and the communication goes ahead, if they are identical.
Also in network devices, such as hubs or routers a large variety of identity comparators is used. However, these functions are always built into microchips and chipsets.
But enough about identity comparators. Next, you look at magnitude comparators...