IBM 2741
Encyclopedia
The IBM 2741 was a printing computer terminal
Computer terminal
A computer terminal is an electronic or electromechanical hardware device that is used for entering data into, and displaying data from, a computer or a computing system...

 introduced in 1965.
It combined a ruggedized Selectric typewriter
IBM Selectric typewriter
The IBM Selectric typewriter was a highly successful model line of electric typewriters introduced by IBM on July 31, 1961.Instead of the "basket" of individual typebars that swung up to strike the ribbon and page in a traditional typewriter, the Selectric had a type element that rotated and...

 mechanism with IBM
IBM
International Business Machines Corporation or IBM is an American multinational technology and consulting corporation headquartered in Armonk, New York, United States. IBM manufactures and sells computer hardware and software, and it offers infrastructure, hosting and consulting services in areas...

 SLT
Solid Logic Technology
Solid Logic Technology was IBM's method for packaging electronic circuitry introduced in 1964 with the IBM System/360 series and related machines. IBM chose to design custom hybrid circuits using discrete, flip chip-mounted, glass-encapsulated transistors and diodes, with silk screened resistors...

 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
Parity bit
A parity bit is a bit that is added to ensure that the number of bits with the value one in a set of bits is even or odd. Parity bits are used as the simplest form of error detecting code....

 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.

The 2741 supplanted the earlier IBM 1050
IBM 1050
IBM 1050 Data Communications System is a computer terminal subsystem to send data to and receive data from another 1050 subsystem or IBM computer in the IBM 1400, IBM 7000 or System/360 series. It first became available in 1963 and was used widely during the 1960s.-General:IBM 1050 Data...

, which was more expensive and cumbersome, in remote terminal applications. The IBM 1050 and variations were frequently used as console devices for computers such as the IBM 1130
IBM 1130
The IBM 1130 Computing System was introduced in 1965. It was IBM's least-expensive computer to date, and was aimed at price-sensitive, computing-intensive technical markets like education and engineering. It succeeded the IBM 1620 in that market segment. The IBM 1800 was a process control variant...

 and IBM System/360. By contrast, the 2741 was primarily focussed on remote terminal applications; the primary initial application for the 2741 was the IBM Administrative Terminal System
IBM Administrative Terminal System
The IBM Administrative Terminal System, also known as ATS/360, was an IBM contributed program which provided, for the end-user customer of IBM System/360 systems, a system which was quite similar to the proprietary IBM Service Bureau Corporation product which ran on IBM 1440 systems or on IBM...

 (ATS/360) (for which the 2741 was initially developed and marketed). ATS was an interactive text editing system implemented in the mid-1960s using IBM System/360 assembler language.

The 2741 then encouraged the development of other remote terminal systems for the IBM System/360. APL\360 and ALGOL 68
ALGOL 68
ALGOL 68 isan imperative computerprogramming language that was conceived as a successor to theALGOL 60 programming language, designed with the goal of a...

 are two early languages that took advantage of the Selectric print mechanism with its relatively large character set and changeable fonts.

The IBM 2741 came in two different varieties, some using "correspondence coding" and the others using "PTT/BCD coding." These referred to the positioning of the characters around the typeball and, therefore, the tilt/rotate codes that had to be applied to the mechanism to produce a given character. A "correspondence coding" machine could use type elements from a standard office Selectric (i.e. elements used for "office correspondence"). "PTT/BCD coding" machines needed special elements, and did not have as wide a variety of fonts available. The IBM 1050 and its derivatives were only available in PTT/BCD coding, so a type element from, say, a System/360 console printer would produce gibberish on a "correspondence coding" 2741 or an office Selectric, and vice versa.

The two varieties of IBM 2741 used different character codes on the serial interface as well, so software in the host computer needed to have a way to distinguish which type of machine each user had.

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.

Keyboard layout with the APL typeball print head inserted:


As a direct result the characters ∨, ∧, ¬, ≠, ≤, ≥, ×, ÷, ⌷, ↑, ↓, ⌊, ⌈ and ⊥ from the APL typeball print head found their way into the ALGOL 68
ALGOL 68
ALGOL 68 isan imperative computerprogramming language that was conceived as a successor to theALGOL 60 programming language, designed with the goal of a...

 programming language standard Final Report (August 1968).

Related machines

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.

IBM sold the underlying Selectric mechanism to other manufacturers, who produced 2741 clones at lower cost.
There were also integrated into larger systems.
For example, the 2741's mechanism formed the principal user interface for a series of machines from the 1960s and 1970s built in the UK by Business Computers Ltd
BCL Molecular
The BCL Molecular 18 was a range of 18-bit computers originally manufactured by Systemation Limited and serviced by Business Mechanisation Limited. The two companies merged in 1968 to form Business Computers Limited - a public limited company. Business Computers Ltd subsequently went into...

.

Decline

The 2741 and similar machines were supplanted by 30 char/s ASCII
ASCII
The American Standard Code for Information Interchange is a character-encoding scheme based on the ordering of the English alphabet. ASCII codes represent text in computers, communications equipment, and other devices that use text...

 terminals using the Xerox
Xerox
Xerox Corporation is an American multinational document management corporation that produced and sells a range of color and black-and-white printers, multifunction systems, photo copiers, digital production printing presses, and related consulting services and supplies...

 Diablo 630
Diablo 630
The Diablo 630 was a daisy wheel printer sold by the Diablo Data Systems division of the Xerox Corporation from 1980. The printer was capable of letter-quality printing; that is, its print quality was equivalent to the quality of an IBM Selectric typewriter, Selectric-based printer, or similar...

 print mechanism. The IBM 3767
IBM 3767
IBM 3767 Communication Terminal is a serial printer terminal that employed wire matrix print-head technology and, for the first time, the Synchronous Data Link Control communications protocol set under IBM's Systems Network Architecture...

which ran at 80 or 120 char/s was an alternate replacement.

External links

The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
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