The space-cadet keyboard was equipped with seven modifier keys: four keys for bucky bits, and three shift keys, called,, and . had been introduced on the earlier Knight keyboard, while and were introduced by this keyboard. Each group was in a row, thus allowing easychording, or pressing of several modifier keys; for example, could be pressed with the fingers of one hand, while the other hand pressed another key. Many keys had three symbols on them, accessible by means of the shift keys: a letter and a symbol on the top, and a Greek letter on the front. For example, the key had a "G" and an up-arrow on the top, and the Greek letter gamma on the front. By pressing this key with one hand while playing an appropriate "chord" with the other hand on the shift keys, the user could get the following results:
Key pressed
Result
g
G
γ
Γ
↑
Each of these might, in addition, be typed with any combination of the,,, and keys. On this keyboard, it is possible to type over 8,000 different characters. This allowed the user to type very complicated mathematical text, and also to have thousands of single-character commands at their disposal. Many users were willing to memorise the command meanings of that many characters if it reduced typing time. This attitude shaped the interface of Emacs; compare the use of the key in vi, due to the convenient position of the key on the ADM-3A terminal. Other users, however, thought that so many bucky bits were overkill, and objected to this design on the grounds that such a keyboard can require three or four hands to operate. As a result of Emacs making frequent use of multiple modifiers, which are easy on the space-cadet keyboard, it is substantially harder to use on modern keyboards, whose layout generally follows the Model MIBM PC keyboard, where the modifier keys are not grouped together and thus are harder to press together. This is also the reason Emacs uses "M-" as the prefix for when describing key presses: the "M-" stood for on the space-cadet keyboard, and when Emacs was ported to PCs, the key was used in place of. This keyboard included a key which had limited application support. It also included four Roman Numeral keys which allowed for easy interaction with lists of four or fewer choices.
