The internet started as a small "net" of interconnected computers, but how were those computers connected? Was a chip manufactured to be installed onto the computer? Was it software?
The wikipedia article on ARPANET explains the earliest architecture. Communication was over leased telephone lines using acoustic modems. Each node was run by a small, specialized computer that did routing. Communication between the routers and the local computers was through a serial port. To read the packets off the serial port, the local machine would have to have some kind of software installed (what we would call today a "tcp/ip stack").