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The IBM 2741 was a printing computer terminal introduced in 1965. Compared to the teletypewriter machines that were commonly used as printing terminals at the time, the 2741 offered slightly higher speed, much higher quality printing, interchangeable type fonts, and both upper and lower case alphabets. It was used primarily with the IBM System/360 series of computers, but was used with other IBM and non-IBM systems where its combination of higher speed and letter-quality output was desirable.〔(【引用サイトリンク】title=DPD Chronology: 1970 )〕 It was influential in the development and popularity of the APL programming language. It was supplanted, starting in the mid-1970s, primarily by printing terminals using daisy wheel mechanisms. == Design == The IBM 2741 combined a ruggedized 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). In contrast to serial terminals employing ASCII code, the most significant data bit of each character was sent first. As with the standard office Selectrics of the day, there were 88 printing characters (not quite enough for the entire ASCII printing character set including the lower case alphabet) plus space and a few nonprinting control codes, more than can be represented with six data bits, so shift characters were used to allow the machine's entire character set to be used. The machine was packaged into its own small desk, giving the appearance of square tabletop with a Selectric typewriter partly sunken into the surface, with the electronics in a vertically oriented chassis at the rear. It supplanted the earlier IBM 1050, which was more expensive and cumbersome, in remote terminal applications. The IBM 1050 and its variations were designed for a higher duty cycle and so were frequently used as console devices for computers such as the IBM 1130 and IBM System/360. By contrast, the 2741 was primarily focused on remote terminal applications. The IBM 2741 came in two different varieties, one using "correspondence coding" and the other 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. The two element types were physically interchangeable, but code-incompatible, so a type element from, say, a System/360 console printer (a variety of IBM 1050) 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. One way this was accomplished was by having the user type a standard command such as "login" immediately after connecting. The host software would recognize which code was used by the value of the characters it received.〔(【引用サイトリンク】first=Thomas )〕 The protocol was simple and symmetric. Each message began with a control character called "circle D" in the documentation, shown as , and ended with a "circle C" . Each message was assumed to begin with the shift mode in lower case. When the other end was sending, the local keyboard was locked. An "attention feature" allowed the operator to interrupt the sending machine and regain control (much in the manner of "control-C" in many ASCII systems) by pressing a special key. Protocol symmetry allowed two 2741s to communicate with each other with no computer in between, but this was a rare configuration. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「IBM 2741」の詳細全文を読む スポンサード リンク
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