Teardown of a 50-Year-Old Modem

Before there was WiFi and Ethernet and cable modems and fiber everywhere, you connected to the Internet and BBSes via phone lines. The acoustically coupled modem was the solution to sending data through the phone lines from 1956 until 1978. The first version of this modem was introduced only a year or so after the Bell 103 modem, the first commercially available modem, and is an excellent example of what can be done with thirteen or so transistors.

Source: hackaday.com