Paper tape.

Since the dawn of telegraph until the early mid 1990’s Paper Tape was used as a code storage solution for computers. Other companies had different types of setups and specs. IBM and HP both used Punch Cards as their variant of paper based storage.

How does Paper Tape work?
Simple, a typical tape reader uses Photo transistors to sense IR light. A punched hole repents a ONE and a non-punched hole is a ZERO. It reads the tape data horizontally. So while the tape is running through the reader and a punched hole lets the IR light hit the Photo-Transistor at a certain Address then it can put the pieces together and get a Binary number for what the Letter or Digit would be.

pp-04

Also there are smaller holes in the middle of the tape that a sprocket will drive the tape. There are different variants such as 5-bit up to 8-bit.

Some people have built DIY readers and will use the smaller sprocket holes as a timing clock pulse. I imagine the electrical mechanical ones had the motor with the drive sprocket timed to work as a clock pulse.

There are many ways to integrate a Paper tape reader to a computer such as injecting the code directly into the Address  BUS and Data BUS that was typically Parallel. Also it could be done via Serial.

The Punch machine came in assortment of flavors. The most common was a Teletype system.

_FLEXO

Typically a programmer would just hit print and the machine would punch out the tape, or the programmer could make it punch the tape in realtime. Then the programmer could use it on a reader and even ran again into a machine to copy the tape.

If you think about it this was a true means of a hard copy however for today’s world for modern software it would take many rolls of tape for a single program. For an example Microsoft Windows is around 50 Million lines of code and Altair BASIC 8K can be stored on a duct tape size roll of paper tape. This is in a span of 40 years. Who knows what will be next in 40 years for data storage. I remember when people said nothing will top the CD. Yet we have Jump Drives and SD cards that are faster and can hold more than a Blu-ray disc.

Reason why I brought all of this up is because I was thinking to make a Tape Reader for my Retro z80 Computer. It’s very simple for the reader but the tape punching would be a major pain to do unless I dished out a few hundred for a punching machine. I could use a non-standard format but I would be reinventing the wheel.

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