The first modems converted U.S. Air Force radar data into sounds and squawked them over phone lines. A receiver then translated the noises back into data. ("Modem" draws its name from the first letters of the words describing the process: MOdulation and DEModulation.) Transmission was slow until the late 1990s, when it hit 56 kbps, fast enough to learn that you've got mail. - Popular Mechanics
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