The Manchester Baby was a serial computer - that is it worked one bit at a time. When you want to add two eight-bit numbers a serial computer does it by adding the first pair of bits, then the next pair and so on. A serial computer is relatively easy to build but it isn’t the natural way to use the inherently parallel storage provided by the CRT store. The Baby used 32 words of 32-bit storage and used CRT storage for its accumulator and its control registers. The only input device was a bank of switches and for output you had to read the dots on the front of the CRT tube - there’s direct machine interaction for you! On June 21, 1948 the first program to run on any stored program computer found the highest factor of an integer. It took 52 minutes and Manchester folklore has it that it was the only program Kilburn ever wrote - the first and his last!

A few words are needed to clarify the position that the Baby holds in the history of computing. The first electronic computer was probably the ENIAC which predated the Baby by two years - but it wasn’t really what we would recognise as a modern computer and more importantly it wasn’t a stored program computer. To program the ENIAC you had to rewire it. The ENIAC’s team started work on a stored program design immediately and despite working hard they didn’t switch on their machine, the EDVAC,  until late 1950 and it had been beaten to the post not only by the Baby in 1948 but by the Cambridge EDSAC in 1949.

Manchester Mark I

There is a lot of weight behind the claim that the first modern digital computers were British but you have to remember that there was a fairly strong two-way communications channel open between the US and UK pioneers. Kilburn certainly knew of, and fully understood, Von Neumann’s logical design for a stored program computer and the CRT storage system and other Manchester developments were used in US designs.

Although the Baby wasn’t really up to being used for real work it was impressive enough to be shown to the outside world - despite Williams' protests. Ferranti, a Manchester electrical engineering firm, came to see the Baby and decided that it was something they were interested in. At the end of 1948 a contract was signed for Ferranti to produce a machine to the design of Professor Williams. The machine was to be paid for by the government and £100,000 was committed to the project.

The Baby was developed beyond the test bed stage into a fully fledged computer - the Manchester Mark I. This was working by April 1949 and it had a very much enhanced design. It had a magnetic drum store and most important of all, two index registers. A third CRT was added. The accumulator was called the A tube and the control register the C tube - so the index register was called the B tube. Today we take index and other address modification registers as part of every machine. In 1949 it was a very new idea.  The Mark I worked at a clock rate that today we would think of as around .5MHz but remember it was a serial machine. An add took 1.2ms and a multiplication took 2.16ms. The Mark I was fast because its store was random access rather than the serial delay line stores used by other machines of its day.

Ferranti built a commercial version of the Mark I but it didn’t really sell well. It was too expensive, too unreliable and needed too much looking after. However Manchester managed to sell time on their Mark I and so fund further development. People queued up to use the Mark I and were prepared to pay £50 per hour. Over 20% of the machine's time was used by industry and commerce.

What struck Kilburn most strongly was the way that much of their time was wasted. A user would turn up with a prepared punch tape. They would feed it in and wait for the results. After that a there would usually be a long pause while the output was studied and corrections worked out. All in all the computer time actually used in a 1 hour session could be very little indeed. The needs of the users certainly made themselves clear to Williams and Kilburn and they decided it was time for another computer. Even so the Mark I was used to solve real problems until 1958 - and amazingly long time for a pioneering machine.

A "packaged" Mark I

The big difference between Manchester and other centres of early development is that they went on. They built the MEG, or Mark II, which became the Ferranti Mercury, then the MUSE which became the Ferranti Atlas and finally the MU5 which became the ICL 2900. These were all well known and successful machines but more importantly they were all pioneers in their own right.

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