Paper Tape

(from a "TrekGame" discussion on RonJandrasi's home page.)

IIRC an awful lot of (punch tapes) used Baudot coding due to their common use in Teletypes. In any event there were many encodings used, so first we'd have to establish which kind of punch tapes you're talking about. Then the protocol would come up...they had a lead-in and a lead-out... -- DougMerritt

My old TrekGame tapes are 7 holes across with a continuous row of alignment holes (smaller) between the 3rd and 4th rows. Readable letters for a program name and date are punched into the beginning, but no printed characters. Don't know if I have the patience to decipher it, but I hate to have information lost. --Ron

Well, the seven rows of holes sound like AsciiCode, 'cause Baudot would be 5-bit, not 7. It occurred to me last night, however, that ASCII might not be good for the structural integrity of the paper tape because there would be so many holes in the 0th, 5th, and 6th rows. About half the zeroth row would be punched; keywords and the names of variables would create runs of holes in the 6th row; all the numerals and most of the symbols would punch the 5th row. Hmm... The good thing is, ASCII would not punch both the 5th and 6th hole for a character because old Basic did not use lower-case characters. The 5-bit Baudot code would probably distribute the holes better, but it's not easy to decipher Baudot by eyeball because the letters and numerals don't go in a nice numerical order. And numbers in Baudot have to be turned on and off. As an aside, the strange ingenuity of the EBCDIC code used in HollerithPunchCards was twofold: the holes ended up distributed well in the rows so as not to weaken the card; the holes were pretty easy to decipher by eyeball if the characters typed across the top of the card were illegible (machine out of ink). -- ElizabethWiethoff

I never knew that EBCDIC encoding was related to punch card integrity!! Elizabeth, you're a wealth of knowledge.. thanks! BTW I had a teacher once who said he saved files in EBCDIC as a down and dirty encryption scheme... --Ron

HollerithPunchCards, and the encoding of information punched into them, have always been about card integrity. That's because Mr. Hollerith designed the cards to be lugged around all over the country by field agents gathering data for the 1890 census. Of course, EBCDIC wasn't invented until later, and so were the tiny machine-punched holes instead of larger hand-punched holes. But still, punch cards were probably less about storing a computer program and more about gathering data, less about careful computer operators and programmers practicing their esoteric arts in an air-conditioned computer room and more about all sorts of people gathering and passing all sorts of information around on its way to the computer room. Fire and water damage aside, the punched cards were designed to withstand human hands, backpacks, envelopes, shirt pockets, shuffling and sorting, throwing into a box, dumping from a box onto the floor--everything but "fold, spindle, or mutilate." As for EBCDIC, there was not 1 hole punched into the card for each EBCDIC bit. There couldn't be, because EBCDIC is an 8-bit code and the punch cards had 12 rows for holes. And yes, all 12 rows were used. If I'm not mistaken, though, no character required more than 3 holes. -- Eliz

E.g. 1-9 for base-1 numeric, plus 3 shift codes to reuse the numeric codes for +/-, alpha, etc.

There were many encoding systems, and many used all 12 rows, but I could have sworn that some common punches of EBCDIC avoided the top rows and used exactly 8 rows. I guess I'm misremembering; although it interferes with the graphics printed on the card (what was the term for that?), clearly it helps with structural integrity.

[lots more at HollerithPunchCard!]

There's a guy who has a script on his site (no, he won't give out the source) which produces standard 5-bit teletype output "tape" images. The site ( was something I stumbled on while doing research into old TTY gear. Yeah, I used to read the stuff right off the tape. -- GarryHamilton

Origin of DELETE

The code of the control character DEL is all ones (except the parity thatis, as usual, unspecified). This is a tradition from the old days of computing (and also from telegraphy), when punched paper tape was an important medium for input/output. When punching information on a paper tape, whenever the user noticed an error, they would delete the bad character by pressing the DEL key on the keyboard. This worked by backspacing the tape and punching a frame of all 1's on top of the holes of the bad character. When reading the tape, the tape reader would simply skip any frame of all 1's.

-- DougMerritt

I wonder though, doesn't that violate the structural integrity thing? Or was the structural integrity issue more limited to hollerith cards? Seems to me this would be an even bigger problem on PaperTape.

Probably. I never used it heavily, but I sure remember a lot of issues with torn paper tape; it didn't take much. I seem to recall that splicing it back together with tape didn't always work, either, since then it tended to jam at the join. Urk.

The thing about DEL being all-holes-punched I think is kind of elegant otherwise, though.

I agree. When I worked with paper tape I was just using it as an archiving media.. I didn't enter stuff directly onto the tape.. I only saved stuff to a tape when I was ending a session. The direct interaction was text on paper via a teletype terminal, so the DEL on pt never occurred.. --Ron

You had RAM, not just paper tape? What a luxury! :-) IIRC the specs we had 128k RAM shared university wide through time sharing.. of course for long term archiving we still chiseled on cave walls...:-,)

A programmer's editor circa 1965:



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