A machine that produces printed copy, character by character, as it is operated. Its essential parts are a keyboard, a set of raised characters or a thermal print head, an inked ribbon, a platen for holding paper, and a mechanism for advancing the position at which successive characters are printed. The QWERTY keyboard (named for the sequence of letters of the top row of the alphabet worked by the left hand) was designed in the 1870s. It contains a complete alphabet, along with numbers and the symbols commonly used in various languages and technical disciplines. The manual typewriter was introduced in 1874, followed by the electrically powered typewriter in 1934. By the late 1970s, electronic typewriters offered memory capability, additional automatic functions, and greater convenience. Further advances in electronic technology led to additional capabilities, including plug-in memory and function diskettes and cartridges, visual displays, nonimpact printing, and communications adapters. Although many typewriters are still in use, computers and word processing software largely have supplanted them.