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Teletype Model 33 from IBM from 1963. Punched tape on the left for storing typed text.

When Computers Had Paper Screens

Before 1969 computers did not have electronic displays like they do today. This might make you wonder how people were able to lookup information on a computer and input data.

They did in fact use something very similar to a type writer called a teletyper (or TTY). Except instead of feeding it one sheet of paper at a time it has a big roll of paper so you could keep typing for a long time.

First a bit of Earlier History…

To put these machines into context, it helps to know some of the history of telegraphs. You have probably heard about morse code. You tap on a telegraph sender to send long or short signals. The telegraph receiver would then make long or short marks on a tape.

Thus the telegraph operator at the other end could look at the strokes on this tape and interpret the morse code. Here is an example of an actual historical telegraph sender and receiver.

People understood that it would be much nicer if one did not have to practice morse code to communicate with a telegraph but instead could simply write letters. This led to the invention of the printing telegraph.

This is what gave rise to teleprinters/teletypers. With these you could type on what looked like a regular type writer, and transmit the message long distance to another teleprinter. This was sent through a system called telex separate from the phone system.

So each teleprinter had their own telex number and you could dial other teleprinters. Because you got charged for the time spent on the line, one did not typically use the communication line interactively. Rather the message got recorded on punched paper type.

When the message was ready you could push a button and the machine would read of the perforated paper tape and send the signals to the receiver.

Early Mainframe Computers

So because teletype/teleprinter machines were already well established and known, it made sense to use these for interacting with mainframe computers. You could connect several of these to each mainframe computer. Since teleprinters were already used across telex networks it also made sense to connect remotely to a mainframe.

This is why old Unix text editors such as ed seems to strange to us today. Like why does it not show us a screen with a cursor we can move around to edit text. It could not do that when Unix was made, because there was no screen you could move a cursor around. What you had, was a teleprinter typing ink letters on a roll of paper.

This may seem excruciatingly awkward to deal with, but compare it to the alternatives. My mother was a journalist back in those days. She wrote her articles on a regular type writer. If she made a mistake, she had to pull out the paper and write the whole article over again.

With the teleprinter interface in contrast you had the option of listing the file you had written. Then you could look over it, locate mistakes and identify which line number and word you had written wrong. Then you could issue a command to ed to substitute that word for the correct one. That was an enormous time savior compared to writing the whole thing over again as your typical journalist or author would have had to do back in those days.

Interactive Computer Graphics on Paper

This sounds like an oxymoron. But you could in fact view, create and edit drawings on paper. Although I’ll leave it to you to decide how interactive it was.

Long before there was electronic screens to show computer graphics many technical professions had a need for this. For instance in the oil industry where I work, geologist would look at logs of well data and maps of the subsurface. They needed to make interpretations of this data and draw trajectories of planned wells, where they believe a fault line runs etc. This was possible. One would use a plotter to draw the vector data.

The lines drawn on paper could then be recorded and transmitted to the mainframe using a digitizer.

These were basically like computer mice with cross hairs you could place right above the point you wanted to record the coordinates of.

For engineering drawings this makes even more sense since these are always made up of basic shapes such as circles, lines and arcs. Such shapes are defined by a few points. If you want to digitize a circle on a drawing e.g. You only need to record 3 different points on the circle because a circle is defined completely by 3 points. Here is video of an engineering drawing being digitized with a lens cursor. In another video there is a demonstration of using a stylus for digitizing machine parts.

So with the combination of plotters and digitizers you have the ability to view and modify vector graphics stored on a mainframe computer.

How About 3D Graphics?

We can print and digitize in 3D as well, so in principle you don’t need a computer screen to do 3D graphics. There are different kinds of 3D digitizers. I am specifically showing a kind here called coordinate measurement machines (CMM) which are based on touching the objects you want to scan.

In the arm it is recorded what angle each joint is at to calculate the coordinate of the tip when you pressed the button to record the point. I think these are interesting to show because in principle they could have made these in the 50s and 60s as well. The laser scanners would have been harder.

If you want to view your scanned models you could in principle 3D print them. With modern 3D printing technology such as Carbon’s Digital Light Synthesis technology, 3D models are printed very fast.

Written by

Geek dad, living in Oslo, Norway with passion for UX, Julia programming, science, teaching, reading and writing.

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