Storing data in waves: Delay line memory

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It’s the ’60s, and you don’t have access to a semiconductor fab to make piles of cheap memory for you, so how could you store data on your computer?

Well, MAKE subscriber Steve points us to one possible solution, courtesy of delay line memories. Rather than having a bunch of individual units that store a bit each, these memory devices work by storing data in sound (compression) waves. The device consists of a long length of wire, with an actuator on one end to vibrate the wire, and a reader on the other end to pick up vibrations. Because the vibrations don’t travel very fast along the wire, you can make a whole bunch of them before the first one reaches the end of the wire, and that becomes the ‘size’ of the memory. Data can be read back by looking for a vibration at a particular time- if there is one, that corresponds to a ‘1’, and if there isn’t, it would be a ‘0’.

It sounds a bit weird, so I like to think of it like this. If you had a hard time remembering things for very long, and happened to live in a cave, you could just shout out what you didn’t want to forget, and a few seconds later you would hear an echo to remind you. Of course, the problem with this is that an echo doesn’t stick around for long, so you would have to shout again every time that you heard the echo, so that you could remember again in a few seconds. Assuming you could keep this up, you would never forget your idea. Of course, that would get really tiring after a while, so you would be much better off just writing it down.

The memory shown above is from a Monroe Epic 3000 calculator, which was apparently the first programmable calculator with a printer built in.