A punched tape is a strip-shaped data carrier made of paper, plastic or a metal-plastic laminate whose information is represented by punched holes. The principle corresponds to a punched card with variable length.
Punched tape was used until the 1990s as a data carrier for teleprinters and computers (usually as an input medium). They are still used today in the control of machine tools.
There are two mechanically compatible strip formats. In both formats, 10 characters (rows) are punched onto one inch (25.4 mm) of perforated strip.
- The punched tape commonly used in teletype technology and early computer technology has a width of 17.4 mm and has 5 parallel data hole positions plus a smaller guide hole located between data holes 3 and 4. The data holes are arranged in a square grid of 2.54 mm = 1/10 inch. Initially, only 32 characters can be encoded on a 5-channel punched strip. With the Baudot code, two special control characters can be used to switch between two code halves, so that theoretically a total of 59 effective characters could be encoded, of which only 54 are used in the common Baudot-Murray code (CCITT-2)
- The perforated strips, which later became widespread mainly in computer technology, have a width of 25.4 mm and have 8 data hole positions. As with the first-mentioned format, the guide hole is located between holes 3 and 4. 256 different characters can be stored on an 8-channel punched strip.