Punched tape

From Academic Kids

Missing image
Tape.jpeg
A roll of 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. (See Jacquard loom).

This led to the concept of communicating 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 were eventually phased out, after many years of use, in the 1990s.

In 1846 Alexander Bain used punched tape to send telegrams.

Punched tape was a standard storage medium for CNC machine tools. Tapes for heavy regular use were made out of plastic (Mylar) to improve their life span.

Use with teleprinters

Missing image
Honolulu_IFSS_Teletype1964.faa.jpg
Paper tape relay operation at FAA's Honolulu flight service station in 1964

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 line charges. Tapes punched at the receiving end could be used to relay messages to another station. Large store and forward networks were devloped using these techniques. Paper tape also was the basis of what may be the single most important invention in cryptography, the Vernam cipher.

Tapes originally had five rows of holes for data. Later tapes had 6, 7 and 8 rows. Text was encoded in several ways. The earliest standard character encoding was Baudot, which dates back to the nineteenth century and had 5 holes. Later standards, such as Fieldata and Flexowriter, had 6 holes. In the early 1960s, the American Standards Association led a project to develop a universal code for data processing, which became know as ASCII. This 8-level code was adopted by some teleprinter users, including ATT (Teletype). Others, such as Telex, stayed with Baudot.

When the first minicomputers were being released, most manufacturers turned to the existing mass-produced ASCII teletypewriters (primarily the ASR33) as a low-cost solution for keyboard input and printer output. 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.

"Wikipedia" in ASCII punched tape code (without a parity bit or with "spacing" parity) appears as follows (created by the BSD ppt program):

 /\/\/\/\/|
|     .   |
|     .   |
| o o .ooo|  W
| oo o.  o|  i
| oo o. oo|  k
| oo o.  o|  i
| ooo .   |  p
| oo  .o o|  e
| oo  .o  |  d
| oo o.  o|  i
| oo  .  o|  a
|    o.o o|  Carriage Return
|    o. o |  Line Feed
|     .   |
|     .   |
|/\/\/\/\/

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. Some systems used fanfold paper tape rather than rolled paper tape. In these systems, no rewinding was necessary nor were any fancy supply reel, takeup reel, or tension arm mechanisms required; the tape merely fed from the supply tank through the reader to the takeup tank, refolding itself back into the exact same form as when it was fed into the reader.

See also

External links

nl:Ponsband no:Hullband nn:Holband

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