IBM 2741
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The 2741 was a low-speed dumb terminal introduced in 1965. It combined a Selectric typewriter mechanism with IBM SLT electronics and an RS-232-C serial interface. It operated at about 14.1 characters per second with a data rate of 134.5 bits/second (one start bit, six data bits, an odd parity bit, and one and a half stop bits). There were 88 graphic characters and so shift characters were used to allow their encoding in six data bits. There were two different models with different encodings of the keyboard which were difficult to distinguish. The Correspondence model could accept type elements from the ordinary office typewriter. The PTT/BCD model had a more limited choice of elements.
The protocol was simple and symmetric. A message began with a circle D control character and ended with a circle C. The message text was initially lower case. When the other end was sending, the local keyboard was locked. Protocol symmetry allowed two 2741s to communicate directly but this was a rare configuration.
It supplanted the earlier IBM 1050 which was more expensive and cumbersome.
The 2741 was important because it encouraged the development of remote terminal systems for the IBM System/360. APL\360 and ALGOL 68 are two early languages that took advantage of the Selectric print mechanism with its relatively large character set and changeable fonts.
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As a direct result the characters ∨, ∧, ¬, ≠, ≤, ≥, ×, ÷, ⌷, ↑, ↓, ⌊, ⌈ and ⊥ from the APL typeball print head found their way into the ALGOL 68 programming lanuage standard Final Report (August 1968).
Some later IBM Selectric-based machines, such as the Communicating Magnetic Card Selectric Typewriter, could emulate the 2741 and could be used in its place.
The 2741 in turn was supplanted by 30 char/s ASCII terminals using the Xerox Diablo 630 print mechanism. The IBM 3767 which ran at 33.3 char/s was an alternate replacement.
