Teleprinter

A teleprinter (or teletypewriter) is a now largely obsolete electro-mechanical typewriter which can be used to communicate typed messages from point to point through a simple electrical communications channel.

It had a very limited character set, and poor print quality. The printer was often linked to a punched tape punch and reader allowing the creation of a message input stream in an offline mode. This was useful for situations in which access to the communication channel was at a premium.

The teleprinter evolved through a series of inventions by a number of engineers, including Royal E. House[?], David Hughes[?], Charles Krum[?] and Emile Baudot.

Teleprinters used the 5-bit Baudot code (also known as IA2) to represent their character set.

The Baudot code was used asychronously with start and stop bits: the asynchronous code design was intimately linked with the start-stop electro-mechanical design of teleprinters. (Early systems had used synchronous codes, but were hard to synchronise mechanically).

A global teleprinter network, called the Telex network, was established in the 1920s, and was used through most of the 20th century for business communications. The main difference from a standard teleprinter is that telex includes a routing network, originally based on pulse-telepone dialing. Telex is still in use for certain applications such as shipping, news, weather reporting and military command. Some business applications are moving to the Internet.

Teleprinters were also used as the first interactive computer terminals, which had no display. The paper tape function was sometimes used to prepare input for the computer session offline, or to capture computer output.

External references:

• telex (http://www.peine.net/telex/)

For information on the development of telegraphy, including the telex network, see telegraphy.