Punched Tape - Tape Formats

Tape Formats

Data was represented by the presence or absence of a hole at a particular location. Tapes originally had five rows of holes for data. Later tapes had six, seven and eight rows. An early electro-mechanical calculating machine, the Automatic Sequence Controlled Calculator or Harvard Mark I, used paper tape with 24 rows. A row of narrower holes that were always punched served to feed the tape, originally using a wheel with radial teeth called a sprocket wheel. Later optical readers used the sprocket holes to generate timing pulses.

Text was encoded in several ways. The earliest standard character encoding was Baudot, which dates back to the nineteenth century and had five holes. Later standards, such as Teletypesetter (TTS), Fieldata and Friden Flexowriter, had six holes. In the early 1960s, the American Standards Association led a project to develop a universal code for data processing, which became known as ASCII. This seven-level code was adopted by some teleprinter users, including AT&T (Teletype). Others, such as Telex, stayed with Baudot.