The LK201 was a detachable computer keyboard introduced by Digital Equipment Corporation of Maynard, Massachusetts in 1982. It was first used by Digital's VT220 ANSI/ASCII terminal and was subsequently used by the Rainbow-100, DECmate-II, and Pro-350 microcomputers and many of Digital's computer workstations such as the VAXstation and DECstation families.
The keyboard layout was new at the time, adding a set of cursor and miscellaneous keys between the main keyboard and the numeric keypad. The cursor keys were arranged in what has now become the standard "Inverted T" arrangement seen on essentially all contemporary full-sized computer keyboards. Ergonomic considerations caused the keyboard to be designed with a very low profile; it was very thin, especially when compared to the keyboard used on the VT100. The keyboard connected using a 4 position modular connector over which flowed 12 volt power and 4800 bit/s asynchronous serial data.
The keyboard also added a Compose key. This allowed the typing of all of the characters in the terminal's extended character set using two-stroke mnemonics to represent the characters. An umlaut, for example, ü could be typed by pressing the following sequence:
- " (double quote, mnemonically like the dots above the umlaut)
An LED on the keyboard indicated an ongoing compose sequence.
At the time of its introduction, the differences between the new layout and the traditional Teletype Model 33 and VT100 layouts proved disruptive, but the LK201's key arrangement has become the de facto standard for all full-sized computer keyboards, differing primarily in the fact that the Compose key has been removed, and that the numeric keypad shows two double-heighth keys instead of one, decreasing the numpad keys number from 18 to 17.
Follow-on keyboards from Digital refined the design introduced with the LK201. One notable departure from the basic LK201 design was a Unix-oriented keyboard, the LK421, that omitted the added middle group of cursor and miscellaneous function keys but included a dedicated Escape Key. Many Unix users preferred a narrower, ASCII-oriented keyboard rather than the rather-wide LK201 arrangement and the Escape Key was essential for several popular Unix editors.
- Jim Burrows. "Inverse-T History".
- Michael Good (1985). "The Use of Logging Data in the Design of a New Text Editor". Proceedings of CHI '85 Human Factors in Computing Systems. Association for Computing Machinery. pp. 93–97.
- BSD documentation on LK201 keyboard
- More pictures of the LK201 including internals
- LK201 Keycode and Keyboard Division Chart (in color) (jpg 67k) (The scancode of Right Shift is xab, not xae which is (Left) Shift only (see the next reference).
- LK201 Keycodes and Keyboard Divisions