Williams tube
From Wikipedia, the free encyclopedia
The Williams tube or (more accurately) the Williams-Kilburn tube (after Freddie Williams and coworker Tom Kilburn), developed about 1946 or 1947, was a cathode ray tube used to store electronic data.
When a dot is drawn on a cathode ray tube, the spot lasts for a time (called "persistance") that depends on the type of phosphor used in the tube. Another side effect is that the area around this dot is slightly changed in electrical charge. By measuring the charge at that spot, by means of a plate placed over the outside of the front of the tube, you have a simple form of memory that lasts for a time depending on the type of phosphor used. Because the charge gradually leaked off, it was necessary to scan the tube periodically and rewrite every dot (similar to the memory refresh cycles of DRAM in modern systems).
Developed at the University of Manchester in England, it provided the medium on which the first ever 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 regarded as extremely unreliable, and touchy. Most working installations had to be "tuned" by hand. In contrast, delay line memory was slower, but quite reliable. This is why delay lines were used in most machines that were regarded as successful.
