At first I thought this was a kind of Williams Tube, an early type of computer memory that used a grid of illuminated dots on a cathode ray tube to store data. However, according to the summary of this paper, it is basically what it looks like: a system that uses a camera to take a picture of an oscilloscope. Which made me wonder why they would call it a “memory” when it’s just a camera.
The reason I think, is that it uses the short term persistence of the oscilloscope image as a sort of buffer. When the event you’re interested in happens it will trigger the camera, giving you an image of the activity from before the event.
This is actually pretty handy and reminds me of the modern high-speed digital video cameras used on nature shows. They have to capture very unpredictable phenomenon that happen incredibly fast. By the time the photographer noticed, the event they care about has already happened. The trick to the cameras is that they are continually recording footage, keeping it for a short time in a buffer and then overwriting it. When an event happens that the photographer wants to capture, he presses the button and the camera just stops throwing away the old footage. This means the actual recording starts a few seconds before the button was pressed. This video from David Attenborough’s Life in the Undergrowth explains it perfectly. (I remembered the clip from watching the “making of” videos when I saw it a few years ago and wanted to link to it with this post. Apparently my google-fu is weak because I just spent the last hour searching before I found the right combination of keywords.)
By the way, if you haven’t seen Life in the Undergrowth, you should get a copy. It is mind-blowing and possibly my favorite nature documentary.
A Machine with a “Memory”
THIS machine has the faculty for picking up the results of electrical disturbances and registering them in its “mind.” A short time later they are illustrated on an oscilloscope, where photographs are made. The entire operation is automatic.