Williams tube

The Williams tube or (more accurately ) the Williams - Kilburn tube (after Frederic Calland Williams and his colleague Tom Kilburn ), developed around 1946 or 1947, is a cathode ray tube, which was to serve as a work in vacuum-tube computer. Independently of and in the same time domain, the Selectron was developed with the same application in the United States.

When a point is projected through a cathode ray tube, is this point, depending on the phosphor used in the tube, for a time visible ( phosphorescence). A side effect is that the area around the point undergoes a slight change of its electric charge. By measurement of the charge at this point, provides a simple way memory for a time which is dependent on the phosphor used endures. Since the charge is gradually lost, it is necessary periodically to read the tube and each point to write again (similar to the refresh cycle of modern DRAMs).

Developed at the University of Manchester in England, it also represented the medium on which the first electronically stored memory program was written in the Manchester Mark I computer. Tom Kilburn wrote a 17- line program to calculate the highest factor of a number.

The Williams tube was considered to be extremely unreliable and sensitive. Most functioning installations had to be fine-tuned by hand. In contrast, the run-time memory was slower, but quite reliable. This is the reason that was used in most machines of the 1940s and 1950s, which were considered successful, a run-time memory. From the mid- 1950s, the core memory triggered from both technologies.