Let’s Listen To A Tape — Paper Tape

These days, data is as likely as not to be “in the cloud.” Otherwise, it’s probably on a USB flash drive or SD card. But in the old days, paper tape was a widespread way to store and retrieve data. A common way to start the day at the office was to toggle in a few dozen bytes of bootloader code, thread a bigger bootloader tape into your TeleType paper tape reader, and then get your coffee while the more capable bootloader clunked its way into memory. Then you could finish your brew while loading the tape with your compiler or whatever you wanted. [Scott Baker] has a Heathkit H8 and decided using a paper tape machine with it and some of his other gear would be fun.

Instead of a TeleType, [Scott] picked up a used paper tape machine from FANUC intended for the CNC industry. They are widely available on the surplus market, although a working machine might run you $500. [Scott] paid $200, so he had some work to do to make the unit operational.

Paper tape had a few varieties. For computer work, you usually had a tape that could hold eight holes across, one for each bit in a byte. However, there are also 6-bit and 5-bit tapes for special purposes or different encodings (old TeleTypes used 5-bit characters in Baudot). The paper choice varied too. You could get plain paper, oiled paper, which maybe didn’t jam as often, and Mylar, which is less likely to shred up when it does jam.

To make things even more difficult, the machines all worked a little differently as well. Sure, punches almost all use solenoids. But the tape transport was sometimes a pinch roller and sometimes a sprocket-style drive. Reading the holes could be done with mechanical contacts or optically. Some punches left little “hanging chads” on the tape, so you didn’t have to empty a confetti box to throw away the chad.

The repair job was interesting. Inside the machine is an 8051 microcontroller. There was no clock, and the circuit used two custom modules. One was simply a crystal, and the other was an oscillator. Removing both allowed a modern can oscillator to replace both modules. The next problem was a fried serial output driver. Replacing that got things working except for random resets due to a faulty brown-out reset circuit. That was easy to fix, too.

Of course, if you are really cheap, it is easy to make a paper tape reader from 8 phototransistors, and pulling tape through by hand isn’t unheard of. It can even talk USB. We’ve even seen a conference badge that can read tapes.

9 thoughts on “Let’s Listen To A Tape — Paper Tape

  1. I remember that rigamarole with paper tape, punch in the bootloader on the ASR 43 connected to the DEC PDP 1104, then we load a short program on a tape that lasted maybe 10 seconds, and once the computer was up we had a big whack of paper tape it took 20 minutes to load for the main program. This was on linear accelerators used in cancer treatment. My job was the final assembly, firing up and troubleshooting the issues on the machine then commissioning it for final acceptance before shipping.

  2. Watching a DDP516’s 1000cps reader operate is entertaining, with the tape is flying horizontally for a couple of metres, and landing in a big “laundry basket”. Just keep your fingers away from the moving tape’s edge!

    5-channel paper tape had multiple encodings. ASCII was a godsend when it arrived!

    Letters and symbols were “multiplexed” onto 32 symbols using “letter shift” and “figure shift” keys/codes. That abomination has been reinvented for tablets; youngsters forget history and condemn users with their abomination.

    1. This is why you need a tape winder for the output and spool for the feed. They can be pretty expensive to buy, for such a simple device, fortunately as such, they are also easy to make. Adding a spring loaded roller or two to take up slack and mitigate any jerky pulling forces is definitely adventurous, not to mention allowing for a leaf switch to stop it in the event of a jam or after finishing a spool of tape.

    2. I own a printing, chadless TT-253/UG “Keyboard Typing Reperforator”. It prints the text along the top of a wider 5-level tape, and the holes are only 3/4 punched, leaving a chad that’s “hinged” on the leading edge. Has a keyboard and a t(printing) tape punch, but no tape reader and no page printer. Kinda neat, but not very useful with optical readers. But I like oddball equipment.

    1. I still have a copy of the exponentially-decaying sine wave “plotted” on the ASR-33. It was coded in FOCAL, copied from my Small Computer Handbook and glued to the inside cover of my CRC Math Tables book.

      Our PDP-8/L had the fancy fast optical paper tape reader, 50 char/sec tape punch (that DEC people could never get fully aligned…).

      A year later, we were granted the greatest gift… an RK05 disk drive. !!! OMG what a beautiful thing!

      Our 8/L also had two DAC channels, which when hooked to an H-P X-Y pen recorder generated several beautiful plots, which I still have though they have faded in the ensuing 48 years.

  3. Paper tape was an ‘upgrade’ from cassette audio for program load and punch on a home brew 8008 system with 2k bytes of ram. I got a rack mounted reader at a surplus shop and a separate punch. The tape boot program was in Eprom.
    DEC had fan fold tape that would fly through their readers neatly collected back in a stack on the output side. It was how we got our 6800 programs loaded from a Dec 10 cross assembler.

    My friend, who was an IBM xsystems programmer did me one better. He interfaced a card reader punch to his IMSAI.

    Things are so much easier now …

Leave a Reply

Please be kind and respectful to help make the comments section excellent. (Comment Policy)

This site uses Akismet to reduce spam. Learn how your comment data is processed.