What Is a Modem in Computer Networking?

A modem is a type of hardware device that converts between analog and digital data in real time for two-way network communication. The term is short for MODulator dEModulator.

History of Modems

The first devices called modems converted digital data for transmission over analog telephone lines. The speed of these modems was historically measured in baud (a unit of measurement named after Emile Baudot), although as computer technology developed, these measures were converted into bits per second (bps).

 The first commercial modems supported a speed of 110 bps and were used by the U.S. department of defense, news services and some large businesses.

Modems gradually became familiar to consumers starting in the late 1970s and through the 1980s, as public message board and news services like CompuServe were built on early Internet infrastructure. Then, with the explosion of the World Wide Web in the mid- and late 1990s, dial-up modems emerged as the primary form of Internet access in many households around the world.Dial-Up Modems

Traditional modems used on dialup networks convert data between the analog form used on telephone lines and the digital form used on computers. An external dial-up modem plugs into a computer and one end and a telephone line on the other end. In the past, some computer makers also integrated internal dial-up modems into their computer designs.

Modern dial-up network modems transmit data at a maximum rate of 56,000 bits per second (56 Kbps).

However, inherent limitations of public telephone networks often limit modem data rates to 33.6 Kbps (or even lower) in practice.

When connecting to a network via a dial-up modem, the devices customarily relay through a speaker the distinctive sounds created by sending digital data over the voice line.

Because the connection process and data patterns are similar each time, hearing the sound pattern helps a user verify whether the connection process is working.

Broadband Modems

A broadband modem like those used for DSL or cable modem Internet access more advanced signaling techniques to achieve dramatically higher network speeds than traditional modems. Broadband modems are sometimes called "digital modems" and those used for traditional dial-up networking "analog modems." Cellular modems are a type of digital modem that establishes Internet connectivity between a mobile device and a cell phone network.

External broadband modems plug into a home broadband router (or other home gateway device) on one end and the external Internet interface (such as a phone or a cable television line) on the other.  Some broadband routers include an integrated modem as a single hardware unit.

Many broadband Internet providers directly supply suitable modem hardware to their customers (often for a monthly fee). However, standard models such as DOCSIS modems can be purchased through retail outlets.