Williams tube, mercury delay-line and two wire delay-line stores, 1950s.
© Science Museum / Science & Society Picture Library
Examples of digital information storage devices used in computers of the 1950s. In the The Williams Tube (top), information is stored as an electrostatic charge held by the phosphor coating on the screen which glows when struck by electrons. The pattern of charges is continuously refreshed and represents the digital information being stored. The operation of delay-line storage devices is based on the fact that sound waves travel more slowly than electrical impulses. Electrical signals are converted to sound waves by magnetic coils at one end and sent down a tube containing mercury, or a nickel wire. These signals are reconverted at the far end to electrical signals. By recirculating the signals continously the device stores information and acts as a memory.