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The Enhanced Manchester Mark I

The Small-Scale Experimental Machine, known as SSEM, or the "Baby", was designed and built at the University of Manchester, and made its first successful run of a program on June 21st 1948. It was the first machine that had all the components now classically regarded as characteristic of the basic computer. Most importantly it was the first computer that could store not only data but any (short!) user program in electronic memory and process it at electronic speed. (Also, the electronic memory was a true Random Access Memory (RAM), in contrast with the other computers being proposed which were based on a much less flexible storage mechanism).

Although the components of the Baby were small and simple, it so clearly demonstrated the potential of the Stored-Program Electronic Computer that it was immediately decided to design and build a more powerful and useable machine, the Manchester Mark 1 Also by October 1948 the Government had requested Ferranti Ltd. to build a commercial machine to this new design.

The Manchester Mark 1 not only expanded the size and power of the basic Baby components but added some important innovations, in particular a magnetic drum for auxiliary storage, the original ancestor of the disc.

The evolution from the Baby to the Mark 1 took place in a number of stages, and by April 1949 an Intermediary Version was available with most of the increased power (though manual intervention was required to make transfers between drum and RAM). In this form it was used for scientific research in the University in 1949. The full facilities of the Manchester Mark 1 were operational by around October 1949.

The Ferranti Mark 1had the same basic architecture as the Manchester Mark 1, but it was better engineered and included a number of enhancements that made it a significantly faster and more powerful machine. It was the world's first commercially available computer, with the first machine delivered in February 1951. The second machine sold publicly went to the University of Toronto in 1952, and was used in the design of the St. Lawrence Seaway.

Ferranti then produced a revised version, the Ferranti Mark 1*, which had essentially the same architecture, but with a reduced but improved order code. It eliminated most of the idiosyncrasies and irritations of the programming conventions and order code of the Mark 1.