IBM Selectric Typewriter - Features and Uses

Features and Uses

The ability to change fonts, combined with the neat regular appearance of the typed page, was revolutionary, and marked the beginning of desktop publishing. Later models with dual pitch (10/12) and built-in correcting tape carried the trend even further. Any typist could produce a polished manuscript.

The possibility to intersperse text in Latin letters with Greek letters and mathematical symbols made the machine especially useful for scientists writing manuscripts that included mathematical formulas. Proper mathematical typesetting was very laborious before the advent of TeX and done only for much-sold textbooks and very prestigious scientific journals. Special type balls also were released for the Athabaskan languages, allowing Navajo and Apache bilingual programs in education to be typed for the first time.

The machine had a feature called "Stroke Storage" that prevented two keys from being depressed simultaneously. When a key was depressed, an interposer, beneath the keylever, was pushed down into a slotted tube full of small metal balls (called the "compensator tube") and spring latched. These balls were adjusted to have enough horizontal space for only one interposer to enter at a time. (Mechanisms much like this were used in keyboards for teleprinters before World War II.) If a typist pressed two keys simultaneously both interposers were blocked from entering the tube. Pressing two keys several milliseconds apart allows the first interposer to enter the tube, tripping a clutch which rotated a fluted shaft driving the interposer horizontally and out of the tube. The powered horizontal motion of the interposer selected the appropriate rotate and tilt of the printhead for character selection, but also made way for the second interposer to enter the tube some milliseconds later, well before the first character had been printed. While a full print cycle was 65 milliseconds this filtering and storage feature allowed the typist to depress keys in a more random fashion and still print the characters in the sequence entered.

The space bar, dash/underscore, index, backspace and line feed repeated when continually held down. This feature was referred to as "Typamatic."