Editing Punched tape (section)

== Formats ==
[[File:Papertape2.jpg|thumb|Diagnostic minicomputer software on fanfold paper tape (1975)]]
[[File:Mylar Punched tape.jpg|thumb|Mylar punched tape was used for durability in industrial applications.]]
Data was represented by the presence or absence of a hole at a particular location. Tapes originally had five rows of holes for data across the width of the tape. Later tapes had more rows. A 1944 electro-mechanical programmable calculating machine, the Automatic Sequence Controlled Calculator or [[Harvard Mark I]], used paper tape with 24 rows,<ref name="Dalakov"/> The [[IBM SSEC|IBM Selective Sequence Electronic Calculator (SSEC)]] used paper tape with 74 rows.<ref>{{cite web| url = https://www.columbia.edu/cu/computinghistory/ssec-tape.html| title = SSEC Tape| last = da Cruz| first = Frank| date = April 2021| website = Columbia University Computing History| access-date = 25 May 2024}}</ref> Australia's 1951 electronic computer, [[CSIRAC]], used {{convert|3|in|mm|adj=on}} wide [[paper tape]] with twelve rows.<ref name="CSIRAC_2010"/>

A row of smaller sprocket holes was always punched to be used to synchronize tape movement. Originally, this was done using a wheel with radial teeth called a [[sprocket|sprocket wheel]]. Later, optical readers made use of the sprocket holes to generate timing pulses. The sprocket holes were slightly closer to one edge of the tape, dividing the tape into unequal widths, to make it unambiguous which way to orient the tape in the reader. The bits on the narrower width of the tape were generally the [[least significant bit]]s when the code was represented as numbers in a digital system.<ref>{{cite web|title=ECMA standard for Data Interchange on Punched Tape|date=November 1965|id=ECMA-10|publisher=European Computer Manufacturers Association|url=http://www.srcf.ucam.org/~jsm28/ECMA-10/|access-date=2003-07-10|archive-url=https://web.archive.org/web/20110927013440/http://www.srcf.ucam.org/~jsm28/ECMA-10/|archive-date=2011-09-27|url-status=dead}}</ref>

=== Materials ===
Many early machines used oiled paper tape, which was pre-impregnated with a light [[machine oil]], to lubricate the reader and punch mechanisms. The oil impregnation usually made the paper somewhat translucent and slippery, and excess oil could transfer to clothing or any surfaces it contacted. Later optical tape readers often specified non-oiled opaque paper tape, which was less prone to depositing oily debris on the optical sensors and causing read errors. Another innovation was fanfold paper tape, which was easier to store compactly and less prone to tangling, as compared to rolled paper tape.

For heavy-duty or repetitive use, polyester [[Mylar]] tape was often used. This tough, durable plastic film was usually thinner than paper tapes, but could still be used in many devices originally designed for paper media. The plastic tape was sometimes transparent, but usually was [[aluminized]] to make it opaque enough for use in high-speed optical readers.

=== Dimensions ===
Tape for punching was usually {{convert|0.00394|in|mm}} thick. The two most common widths were {{convert|11/16|in|mm}} for five bit codes, and {{convert|1|in|mm}} for tapes with six or more bits. Hole spacing was {{convert|0.1|in|mm}} in both directions. Data holes were {{convert|0.072|in|mm}} in diameter; sprocket feed holes were {{convert|0.046|in|mm}}.<ref>
{{Citation | last = Lancaster | first = Don | title = TV Typewriter Cookbook | publisher = Synergetics SP Press | year = 2010 | page = 211 | url = https://www.tinaja.com/ebooks/tvtcb.pdf }}</ref>

=== Chadless tape ===
[[file:1980-Paper Tape fromTeletype (chadless, 5-level Baudot)-02.jpg|thumb|left|Chadless 5-level Baudot paper tape {{c.|1975–1980}} punched at Teletype Corp]]
Most tape-punching equipment used solid circular punches to create holes in the tape. This process created "[[chad (paper)|chad]]", or small circular pieces of paper. Managing the disposal of chad was an annoying and complex problem, as the tiny paper pieces had a tendency to escape containment and to interfere with the other electromechanical parts of the teleprinter equipment. Chad from oiled paper tape was particularly problematic, as it tended to clump and build up, rather than flowing freely into a collection container.

A variation on the tape punch was a device called a ''Chadless Printing Reperforator''. This machine would punch a received teleprinter signal into tape and print the message on it at the same time, using a printing mechanism similar to that of an ordinary page printer. The tape punch, rather than punching out the usual round holes, would instead punch little U-shaped cuts in the paper, so that no [[chad (paper)|chad]] would be produced; the "hole" was still filled with a little paper trap-door. By not fully punching out the hole, the printing on the paper remained intact and legible. This enabled operators to read the tape without having to decipher the holes, which would facilitate relaying the message on to another station in the network. Also, there was no "chad box" to empty from time to time.

A disadvantage to this technology was that, once punched, chadless tape did not roll up well for storage, because the protruding flaps of paper would catch on the next layer of tape so it could not be coiled up tightly. Another disadvantage that emerged in time, was that there was no reliable way to read chadless tape in later high-speed readers which used optical sensing. However, the mechanical tape readers used in most standard-speed equipment had no problem with chadless tape, because they sensed the holes by means of blunt spring-loaded mechanical sensing pins, which easily pushed the paper flaps out of the way.