return to What makes the 1401 so interesting
by LaFarr Stuart, died July 26, 2021
"Paper Tape" First Machinable I/OLast Up date: 2006 August 18
Page started: 2006 August 18
I can give a little info: In the early days of computers, virtually every computer maker, except IBM, introduced their computers using punch paper tape, because mechanically it was so easy to handle compared to picking up cards one at a time. Even IBM, who produced punched card equipment for years before there was any thought of computers, introduced their first smaller computer "The IBM 1620" with punched paper tape. After it was proven successful they provided a card reader/punch for the 1620.
At first it was 5-level tape, 5 round holes and a smaller "sprocket hole" across a tape about 3/4 inch wide, and latter 8-level on a tape about an inch wide. Paper tape punches were available in both "chad" and "chad-less" the chad-less did not fully punch the little round hole, only about 3/4 of it so the chad stayed with the tape. Chad-less tape did not have to have mechanisms to collect the chad, but it only worked with mechanical readers that "felt" the hole with a little pin; like the readers on the popular ASR-33 & 35 Teletypes. Teletypes, or Flexowriters (which used 8-level tape, but with different combinations of holes for the characters) were the "Consoles" for every computer except those made by IBM. Flexowriters were far less popular, and the punch codes of the Teletypes evolved into what we now call ASCII. Optically, sensing the hole could be much faster, so chad-less tape punches were never popular on computers. (I think they were used by Western Union??)
Frequently paper tape info was read, punched and sent serially at 50 or 75 baud (5-level + 1 start and 2 stop bits) when 8-level tape came in the TTY's read, punched and sent at 110 baud. There was still a start bit and 2 stop bits, thus transmitting ten 8-bit characters per second. Actual information was not quite this fast because each line was terminated by three characters: CR, LF, and a Rub-Out. The Rub-Out was required to allow time for the print mechanism to move to the left margin. A few people, incorrectly used a null instead of the Rub-Out. (I could explain the reason the null was a bad choice if you are interested.)
Eventually, paper tape punches were available that could punch at 75 characters per second. (In the late 1950's such a punch cost in the neighborhood of $4000 or about twice the price of an automobile.) Some companies tried to make punches that went at 100 characters per second for about twice the price; but as far as I know they were never very reliable. ???
Paper tape readers using optical sensing could go faster. (The main problem was stopping and starting the tape.) Reading at 300, 500, and 1000 characters per second was quite common. But, this had some problems, usually caused by dust (from the paper) collecting on the optical sensors. A company in Florida made a tape reader that sensed the hole by having low pressure air and the hole/no hole would turn the air flow on or off. They called this anemometer sensing. What they used was an electric filament in the air flow tube and the moving air would cool the filament and change its' resistance which could be detected electronically. The filament was operated at near red hot, so even if any paper dust was flipped upstream in the air flow it would be burned off. Using anemometer sensing they were able to read tape at 1000 characters per second. And, they could read chad-less tape! But by the time this technology was developed paper tape was on its way out.
Computers were no longer scientific novelties. They had become working machines, and punched cards vastly more flexible, already established in business data processing became the norm. Keypunches and card equipment was the only way to go, until the world became slap-happy with CRT's and mice.
I have given you this much detail, because most "modern" computer historians (Including most of the people at the Computer History Museum) don't realize how significant paper tape was in early computers. It is hardly mentioned or displayed at CHM. Which I feel is a major oversight.