International Telegraph Alphabet No. 2

A five-unit code that carried most of the world’s printed telegraph traffic for half a century, from teleprinter networks to telex and radioteletype.

Five-track paper tape with the holes for I, T, A, figure shift and 2 — The letters I, T and A, a figure shift, and the digit 2, punched in five tracks. A hole is the “Z” condition; the small holes in the middle row only move the tape.

In one paragraph

Each character is a group of five on/off elements, so the code has 2⁵ = 32 combinations. That is too few for letters, digits and punctuation together, so two of the combinations are shift signals: after LTRS the receiver prints letters, after FIGS it prints digits and signs from the same patterns. The code descends from Émile Baudot’s telegraph code of the 1870s and Donald Murray’s keyboard version of 1901, and today it is maintained by the International Telecommunication Union as Recommendation S.1.

Quick facts

Units per character	5 (plus start and stop elements on a line)
Combinations	32, read in letter case or figure case
Printable characters	26 letters, 10 digits, 11 signs, plus 3 positions left for national use
Shift signals	LTRS (combination 29), FIGS (combination 30)
Standard	ITU-T Recommendation S.1 (current text 1988)
Successor	International Alphabet No. 5, the international form of ASCII

Where to go next

The full code table, with the hole pattern of every combination.
A short history from the printing telegraph to the computer terminal.
Related topics: start-stop transmission, the baud, telex, radioteletype and paper tape.