Notes and Reflections on Books and Media
by Hannah Leitheiser
Turing's Cathedral: The Origins of the Digital Universe
The experimental discovery that [CRT] tubes exhibit storage phenomena appears to have been made towards the end of the war. Williams and Kilburn were able to store a 32 by 32 array of charge spots on the face of a single cathode ray tube.
Using inexpensive off-the-shelf oscilloscope tubes...a sequence of pulses in time could be converted to a pattern of spots in space and stored indefinitely as long as the pattern were regenerated periodically by a trace from an electron beam. The state of an individual spot could be distinguished by interrogating that location with a short pulse and noting the character of a secondary current of less than a millivolt induced in a wire screen attached to the outside face of the tube.
...This secondary emission effect can be visualized by imagining a 32 by 32 array of beer glasses sitting in a big kitchen sink and being sprayed with water from a garden hose. With a very sensitive drain in the sink that produces a detectable signal. [If you spray a full glass, it will end up being a bit less full after being sprayed, meaning more water at the drain than when spraying an empty glass.] - George Dyson , Turing's Cathedral: The Origins of the Digital Universe (2012)