[FOM] Difference Engine

[José Félix Costa]

Randall Holmes: «It should be noted that the Babbage engines are not all the
same thing:  the Difference Engine which has actually been built is probably
not Turing complete, while the Analytical Engine, in principle a general
purpose computer, has never been built.»

Yes, you're right. Indeed, a part of the Analytical Engine was built by
Babbage himself, as the Difference Engine Nº 1. Difference Engine Nº 2 was
built by Doron Swade and his team (at Margarette Tatcher's time).

Gandy's article in Herken's (ed) is very good as general reference. Many
thanks to Panu Raatikainen.

The insistence in finding again the paper (I read it!) on Turing
completeness of either the Analytical Engine or either the Difference Engine
is because I wanted to use it as reference and tool to start a new class.
But as we say «whatever is alive soon or later appears».

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J. Felix Costa
Departamento de Matematica
Instituto Superior Tecnico
Av. Rovisco Pais, 1049-001 Lisboa, PORTUGAL
tel:      351 - 21 - 841 71 45
fax:     351 - 21 - 841 75 98
e-mail:   fgc at math.ist.utl.pt
www:    http://fgc.math.ist.utl.pt/jfc.htm
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