Williams tube
Williams tubes were the first true random-access memory device. The Williams tube displays a grid of dots on a cathode ray tube (CRT), creating 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. Frederic Calland Williams and Tom Kilburn applied for patents for the Williams Tube in 1946. The Williams Tube was much faster than the delay line, but suffered from reliability problems. The UNIVAC 1103 used 36 Williams Tubes with a capacity of 1024 bits each, giving a total random access memory of 1024 words of 36 bits each. The access time for Williams Tube memory on the IBM 701 was 30 microseconds.