Every computer connected to the Internet has a unique address.
Examples are Bitnet and uucp. These other networks may be gatewayed to the Internet and may be able to exchange electronic mail with Internet-connected systems. However, computers on these other networks typically will not have access to the wide range of services available to computers on the Internet proper. Each computer on the Internet has a unique address called its fully-qualified domain name. This name serves to identify each computer and network from all of the other computers and networks on the Internet.