|ESK relay, see https://de.wikipedia.org/wiki/ESK-Relais|
A later model was the Einheits-Postmodem (“standard postal modem”) D 200 S. Here you see a “D200S 03” with the handwritten remark “300 Baud”*), sized about 60 cm × 30 cm × 20 cm – 60 cm being today’s standard dishwasher size. The 200 and 300 baud came from an extra hardware plugin to clock for a then asynchronous transmission.
|Harald Schummy, Signalübertragung, p 350, 2013|
That said, here comes the story. The Technical University of Berlin’s mainframe ICL 1904 back in in 1968, when we were allowed to use it at night, had a dial-in modem. I’m 80 percent sure. If that’s wrong you must transpose this story to the time of time sharing Basic systems (60s, 70s) that we supported at HP, or to private mail boxes like Zerberus – which I used – or Fido, both 1984. For more on Berlin’s ICL see my “listening to computer bugs”.
When you connect an analog modem to a computer you hear strange sounds at the beginning, while the modern modems agree on a mutual speed and transmission type. Of course you can record this sound on a tape recorder.
With the Hayes command M2 you cuuld tell a modem to leave on its loudspeaker. So you heared it doing its job all the time. Our system had a command to the operating system to print a message on the console, like machine room to bridge on a ship. Today that was the Windows net send command. So I could dial up the mainframe from outside, and for example ask the operator to return my phone call. I tape recorded this short digital dialogue.
Playing back the sound track into a telephone’s microphone – without a local modem attatched – I got the message through equally easy, naturally giving just the one callback number I had recorded. It worked. (Young reader: Ask yourself, why I didn’t I send a SMS?)
For more about “our” ICL 1904 read Listening to Computer Bugs.
Another story: https://blogabissl.blogspot.com/2017/10/how-i-tried-to-trick-computer.html#retention
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