A modem (modulator-demodulator) is a device that modulates one or more carrier waves to encode digital information for transmission and demodulates signals to decode the transmitted information. Modems can also be used to multiplex signals.

The most common use for modems is to provide a means of connecting a computer to the public telephone network so that it can access the Internet, by using an analog telephone line. A modem can also be used to connect a computer to a private network, such as a company’s internal network.

The history of modems begins with the invention of the telegraph in …