From Baby to Mark I
Written by Historian   
Wednesday, 28 November 2012
Article Index
From Baby to Mark I
Small-Scale Experimental Machine
A Serial Computer

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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.

Manchester Mark I

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.

 

Baby Mark I in use

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. For this next part of the story see Manchester Computers of the 1950s.

 

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