Williams Tube RAM

One of the early attempts to create RAM in computers based on the EDVAC stored-program architecture.
Worked by displaying a grid of dots on a cathode-ray tube ("screen")
Due to the way CRTs work, this creates a small charge of static electricity over each dot. The charge at the location of each of the dots is read by a thin metal sheet just in front of the display.
Each dot position could be written to and read from and the pattern was constantly refreshed as the dots would fade over time.