Photo of a Williams-Kilburn tube from an IBM 701

"Williams–Kilburn tube" or "Williams tube", from an IBM 701 at the Computer History Museum.

Detail map of Manchester, England, United Kingdom Overview map of Manchester, England, United Kingdom

A: Manchester, England, United Kingdom

The Williams Tube and the "Manchester Baby," the First Operational Stored-Program Computer Runs its First Program


In July 1946 mathematician Max Newman founded the computer laboratory at Manchester University via a grant from the Royal Society. Early on engineers in the department recognized that building an electronic memory would be the most difficult task in building a stored-program computer. In June 1946, English engineer F.C. (Freddie) Williams had begun research on the storage of both analog and digital information on a cathode ray tube at the Telecommunications Research Establishment. By November 1946 he was able to store a single bit (with the "anticipation" method), based around a standard radar CRT, and filed a provisional patent for the mechanism in December 1946.

"In December 1946 Freddie Williams was appointed to a chair at the University of Manchester, and left TRE. However both he and TRE wanted the research to continue, so Tom Kilburn, who was in his group at TRE, was seconded to the University of Manchester to continue the work with Freddie Williams on digital CRT storage. A Scientific Officer from TRE was also seconded full time to help him, initially Arthur Marsh, who left after a few months, and was replaced in the summer of 1947 by Geoff Tootill.

"By March 1947 Tom Kilburn had discovered a different and better method of storing information, more suited to storing a large number of bits on the same tube. By November 1947 they had succeeded in storing 2048 bits for a period of hours, having investigated a number of variations on storing a set of bits (dot-dash, dash-dot, defocus-focus, focus-defocus)" (, accessed 10-09-2011).

"The Williams tube tended to become unreliable with age, and most working installations had to be "tuned" by hand. By contrast, mercury delay line memory was slower and also needed hand tuning, but it did not age as badly and enjoyed some success in early digital electronic computing despite its data rate, weight, cost, thermal and toxicity problems. However, the Manchester Mark 1 was successfully commercialised as the Ferranti Mark 1. Some early computers in the USA also used the Williams tube, including the IAS machine, originally designed for Selectron tube memory, the UNIVAC 1103, IBM 701, IBM 702 and the Standards Western Automatic Computer (SWAC). Williams tubes were also used in the Soviet computer, Strela-1" (Wikipedia article on Williams Tube, accessed 10-09-2011).

After two years of research and development, on June 21, 1948 the Manchester Small Scale Experimental Machine,or  Manchester "Baby" prototype computer (Manchester Baby), ran its first program, written by Tom Kilburn. This small pilot version of a larger computer was the first stored-program electronic digital computer. It operated for only a short time.  The machine was built at the Victoria University of Manchester in England by Frederic C. Williams, Tom Kilburn and Geoff Tootill to test the Williams-Kilburn cathode ray tube (CRT) memory (Williams tube).

"The machine was not intended to be a practical computer but was instead designed as a testbed for the Williams tube, an early form of computer memory. Although considered 'small and primitive' by the standards of its time, it was the first working machine to contain all of the elements essential to a modern electronic computer. As soon as the SSEM had demonstrated the feasibility of its design, a project was initiated at the university to develop it into a more usable computer, the Manchester Mark 1. The Mark 1 in turn quickly became the prototype for the Ferranti Mark 1, the world's first commercially available general-purpose computer.

"The SSEM had a 32-bit word length and a memory of 32 words. As it was designed to be the simplest possible stored-program computer, the only arithmetic operations implemented in hardware were subtraction and negation; other arithmetic operations were implemented in software. The first of three programs written for the machine found the highest proper divisor of 218 (262,144), a calculation it was known would take a long time to run—and so prove the computer's reliability—by testing every integer from 218 − 1 downwards, as divisions had to be implemented by repeated subtractions of the divisor. The program consisted of 17 instructions and ran for 52 minutes before reaching the correct answer of 131,072, after the SSEM had performed 3.5 million operations (for an effective CPU speed of 1.1 kIPS)" (Wikipedia article Manchester Small Scale Experimental Machine, accessed 10-09-2011).

None of the original Manchester Baby exists; however, a working replica 5.2 meters long and 1 ton in weight is on display at the Manchester Museum of Science and Industry (MOSI). In June 2013 its operation was demonstrated every Tuesday, Wednesday and Thursday from 11AM to 3PM. Here is a video based on the replica:

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