Difference
Engine the first known
mechanical computer
Before the widespread
availability of dependable mechanical, and,
later, electronic calculators, scientists,
astronomers, navigators, actuaries, bankers, etc.
relied for the most part on printed mathematical
tables to perform calculations requiring more
than a few figures of accuracy. The repetitive
calculations for these tables were performed by
hand by people called "computers" and
results were then copied and set in loose type
for printing. Mistakes were common. Charles
Babbage, an English
mathematician and inventor, sought to build an
automatic calculating machine that would
eliminate all these sources of inaccuracy. It was
his belief that the "unerring certainty of
mechanism" would free calculation of human
error, and having the machine print the results
automatically would eliminate the risk of
mistakes in manual transcription and typesetting,
and it was this belief that led him to design the
Difference Engine.
The
Difference Engine was conceived to calculate and
automatically print errorfree mathematical
tables. It is so named because of the
mathematical principle upon which it is based,
the method of finite differences. The advantage
of the method is that it allows complex
mathematical expressions to be calculated using
simple addition only, without the need for
multiplication and division which would
ordinarily be required.
Babbage began working on Difference Engine No.
1 in the early 1820's, but the machine was never
completed. The project was abandoned in 1833
after a dispute with the engineer, Joseph
Clement, who had been engaged to build the
machine. About oneseventh of the engine had been
assembled as a demonstration piece by Clement in
1832, and this portion of the engine is the first
known automatic calculator. It is automatic in
the sense that for the first time mathematical
rule was incorporated directly into the mechanism
 the operator did not need to understand the
mechanical or logical principles of achieve
useful (and accurate) results. All that was
required was to turn the handle and the machine
did the rest.
The Difference Engine is capable of a fixed
set of operations determined by its wheel work.
Babbage's Analytical Engine, however, conceived
in 1834, has features that are amazingly similar
to those of a modern electronic computer. The
Analytical Engine was programmable using punched
cards, had a repertoire of basic operations
(multiplication, division, addition and
subtraction), and could automatically execute
sequences of these operations in any order. The
"mill," where information was
processed, was physically separate from the
"store" or memory where information was
kept. The separation of "store" and
"mill" (today called the central
processor) is a feature that has dominated the
design of the electronic computer since the
mid1940's. Designs for the Analytical Engine
were highly developed, but no Analytical Machine
was ever actually built.
Cossons, Neil Making of the Modern
World, Milestones of Science and Technology
London: John Murray (Publishers) Ltd., 1992
Charles
Babbage
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