Linotype machines cast lines of type as a single block of print, hence their name. Invented in 1884, they provided a keyboard interface to a hot metal typesetting process. The operator needed only type out what was to appear on the page, and printing blocks were cast on the fly. The keyboard layout was optimised by letter frequency, with separate sections for uppercase (left), lowercase (right) and and numbers and symbols (centre); each section also contained various other unrelated keys. All functionality was mechanical, with no electronics involved.
IBM’s Selectric was a fully mechanical electric typewriter. The intricate and complex printing mechanism was free from the tendency of manual typewriters to suffer jammed typebars, and the interchangeable typing elements allowed the typeface and symbol repertoire to be fully independent of the device itself. The use of a spherical typing element required an encoding and actuation process, and this was entirely mechanical, driven in part by an electric motor. The encoding process resulted in a non-linear feel to keystrokes, that was found to be so desirable that it influenced the introduction of tactile keyswitches in electronically-encoded keyboards.