A now-legendary device used on MIT LISP machines, which inspired several still-current jargon terms and influenced the design of EMACS. It was equipped with no fewer than seven shift keys: four keys for bucky bits (‘control’, ‘meta’, ‘hyper’, and ‘super’) and three regular shift keys, called ‘shift’, ‘top’, and ‘front’. Many keys had three symbols on them: a letter and a symbol on the top, and a Greek letter on the front. For example, the ‘L’ key had an ‘L’ and a two-way arrow on the top, and the Greek letter lambda on the front. By pressing this key with the right hand while playing an appropriate ‘chord’ with the left hand on the shift keys, you could get the following results:
|top-L||⇔ (front and shift are ignored)|
And of course each of these might also be typed with any combination of the control, meta, hyper, and super keys. On this keyboard, you could type over 8000 different characters! This allowed the user to type very complicated mathematical text, and also to have thousands of single-character commands at his disposal. The keyboard of the Symbolics Lisp machine was a simplified version, lacking Top and Front keys, that could only send about 2000 characters.
Many hackers were actually willing to memorize the command meanings of that many characters if it reduced typing time (this attitude obviously shaped the interface of EMACS). Other hackers, however, thought having that many bucky bits was overkill, and objected that such a keyboard can require three or four hands to operate. See bucky bits, cokebottle, double bucky, meta bit, quadruple bucky.
(Some relatively bad photographs of the earlier, more elaborate version are available on the Web.).
Note: early versions of this entry incorrectly identified the space-cadet keyboard with the Knight keyboard. Though both were designed by Tom Knight, the latter term was properly applied only to a keyboard used for ITS on the PDP-10 and modeled on the Stanford keyboard (as described under bucky bits). The true space-cadet keyboard evolved from the first Knight keyboard.