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 as early as the 18th century as wooden plates strung together to control looms.
Punched tape formats
There are two mutually mechanically compatible tape formats:
- The perforated tape, commonly used in teletype and early computer technology, is 17.4 mm wide 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.
- The later punched tape, which was mainly used in computer technology, has a width of 25.4 mm and has 8 data hole positions. As with the first format, the guide hole is located between holes 3 and 4. In both formats, 10 characters (rows) are punched on one inch (25.4 mm) of paper tape.
The two perforated tape formats are thus congruent in the width of the narrower strip when superimposed.
On an 8-channel punched tape, 256 different characters can be stored, on a 5-channel punched tape initially only 32.
With the Baudot code, two special control characters can be used to switch between two halves of the code, so that a total of 59 effective characters can be encoded.