Modem operations

Modems were first introduced as a part of the 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 ticketting offices, tied to a central computer that managed availability and scheduling. The system, known as Sabre, is the distant parent of today's SABRE system.
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, 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 lines for 2400 bit/s operation.
The next major advance in modems was the Hayes Smartmodem, introduced in 1981 by Hayes Communications. The Smartmodem was a simple 300 bit/s modem using the Bell 103 signaling standards, but attached to a small controller that let the computer send commands to it to operate the phone line.
Prior to the Smartmodem, modems almost universally required a two-step process to activate...

Daugiau informacijos...

★ Klientai rekomenduoja

Šį rašto darbą rekomenduoja mūsų klientai. Ką tai reiškia?

Mūsų svetainėje pateikiama dešimtys tūkstančių skirtingų rašto darbų, kuriuos įkėlė daugybė moksleivių ir studentų su skirtingais gabumais. Būtent šis rašto darbas yra patikrintas specialistų ir rekomenduojamas kitų klientų, kurie po atsisiuntimo įvertino šį mokslo darbą teigiamai. Todėl galite būti tikri, kad šis pasirinkimas geriausias!