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==History==
[[Image:BellSystemDataphone1957.jpg|thumb|200px|1957 AT&T Dataphone]]Modems were first introduced as a part of the [[Semi Automatic Ground Environment|SAGE]] air-defense system in the 1950s, connecting terminals located at various airbases, radar sites and command-and-control centers to the SAGE director centers scattered around the US and Canada. SAGE ran on dedicated communications lines, but the devices at either end were otherwise similar in concept to today's modems. [[IBM]] was the primary contractor for both the computers and the modems used in the SAGE system. A few years later a chance meeting between the CEO of [[American Airlines]] and a regional manager of IBM led to a "mini-SAGE" being developed as an automated airline ticketing system. In this case the terminals were located at ticketing offices, tied to a central computer that managed availability and scheduling. The system, known as [[Sabre (computer system)|Sabre]], is the distant parent of today's SABRE system. The [[AT&T]] Dataphone was another pioneering early data-transfer service using telephone lines to transmit business information, such as inventory levels.
By the early 1960s commercial computer use had bloomed, due in no small part to the developments above, and in 1962 [[AT&T]] released the first commercial modem, the [[Bell 103]]. Using [[frequency-shift keying]], where two tones are used to represent the 1's and 0's of digital data, the 103 had a transmission rate of 300 bit/s. Only a short time later they released the [[Bell 212]] modem, switching to the more reliable [[phase-shift keying]] system and increasing the data rate to 1200 bit/s. The similar [[Bell 201]] system used both sets of signals (send and receive) on 4-wire [[leased line]]s for 2400 bit/s operation.
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