The Linotype machine (// LYNE-ə-type) was a "line casting" machine used in printing sold by the Mergenthaler Linotype Company and related companies. It was a hot metal typesetting system that cast blocks of metal type for individual uses. Linotype became one of the mainstay methods to set type, especially small-size body text, for newspapers, magazines, and posters from the late 19th century to the 1970s and 1980s, when it was largely replaced by phototypesetting and computer typesetting. The name of the machine comes from the fact that it produces an entire line of metal type at once, hence a line-o'-type, a significant improvement over the previous industry standard, i.e., manual, letter-by-letter typesetting using a composing stick and shallow subdivided trays, called "cases".
The linotype machine operator enters text on a 90-character keyboard. The machine assembles matrices, which are molds for the letter forms, in a line. The assembled line is then cast as a single piece, called a slug, from molten type metal in a process known as hot metal typesetting. The matrices are then returned to the type magazine from which they came, to be reused later. This allows much faster typesetting and composition than original hand composition in which operators place down one pre-cast glyph (metal letter, punctuation mark or space) at a time.
The machine revolutionized typesetting and with it especially newspaper publishing, making it possible for a relatively small number of operators to set type for many pages on a daily basis. Ottmar Mergenthaler invented the linotype in 1884.
In typesetting, it is sometimes necessary to use characters that are uncommon or obscure enough that it does not make sense to assign them to a magazine channel. These characters are referred to as pi characters or sorts ("pi" in this case refers to an obscure printer's term relating to loose or spilled type). Footnote marks, rarely used fractions, and mathematical symbols are examples of pi characters. In the linotype machine, a pi matrix has all teeth present (code 127, no teeth cut away) so it will not drop from the distributor bar and will not be released into either the main or the auxiliary magazine. Instead, it travels all the way to the end and into the flexible metal tube called the pi chute and is then lined up in the sorts stacker, available for further use.