Punched tape

Punched tape is an old-fashioned form of data storage, consisting of a long strip of paper in which holes are punched to store data.

The earliest forms of punched tape come from weaving looms and embroidery, where cards with simple instructions about a machine's intended movements were first fed individually as instructions, then controlled by instruction cards, and later were fed as a string of connected cards.

This led to the concept of communicating analog data not as a stream of individual cards, but one "continuous card", or a tape. Many professional embroidery operations still refer to those individuals who create the designs and machine patterns as "punchers", even though punched cards, and paper tape, was eventually phased out, after many years of use, in the 1990s.

Punched tape was eventually also used as a way of storing messages for teletypewriters. The idea was to type in the message to the paper tape, and then send the message at "high speed" from the tape. The tape reader could "type" the message faster than a typical human operator, thus saving on phone bills. Text was encoded in two common standards. The Baudot which had 5 holes and the ASCII which had 8 holes.

When the first computers were being released many turned to the teletypewriter as a low-cost solution for printer output. This is why computers today still use ASCII. As a side effect the punched tape readers became a popular medium for low cost storage, and it was common to find a selection of tapes containing useful program in most computer installations.

In the late 1960s to early 1970s, the ASR33 was a very popular teletype. It had a built in paper tape reader and tape punch (8 hole ASCII). It could read/punch tape at the speed of 10 characters per second. The ASR33 tape reader was purely mechanical; 8 spring loaded fingers would be thrust into the tape (one character at a time), an assortment of rods and levers would sense how high the finger rose, which told it if there was a hole in the tape at that position. Later on photo readers that used light sensors could work in much higher speeds.

"BambooWeb" in punched tape code (ASCII) appears as the following (created by the BSD ppt program):

The two biggest problems with paper tape were

• Reliability. It was common practice to follow each mechanical copying of a tape with a manual hole by hole comparison. See also chad (the little pieces of paper punched out of the tape).
• Rewinding the tape was difficult and prone to problems. Great care was needed to avoid tearing the tape.

See also: punch card, chadless tape