Analytical engine





The analytical engine, an important step in the history of computers, is the
design of a mechanical, modern general purpose computer by the British
professor of mathematics Charles Babbage. It was first described in 1837,
but Babbage continued to work on his design throughout his life, which ended
in 1871. Because of financial and technical problems, the engine was never
actually built. It is generally acknowledged however that the design was
correct and that the engine would have worked. Comparable general purpose
computers did not come into existence until about 100 years later.

Babbage started out by constructing his Difference engine, a mechanical
special purpose computer designed to tabulate logarithms and trigonometric
functions by evaluating approximating polynomials. When he realized that a
much more general design was possible, he started to work on the analytical engine.

The machine was to be powered by a steam engine and would have been over 30
metres long and 10 metres wide. The input (programs and data) was provided
to the machine on punch cards, a method being used at the time to direct
mechanical looms. For output, the machine was planned to have a printer, a
curve plotter and a bell. The machine could also punch numbers onto cards to
be read in later. It employed ordinary base-10 fixed point arithmetic. There
was a store capable of holding 1000 numbers of 50 digits each. An
arithmetical unit (called the "mill") was able to perform all four
arithmetical operations.

The programming language employed was akin to modern day assembly languages.
Loops and conditional branching were possible. Three different types of
punch cards were used: one for arithmetical operations, one for numerical
constants, and one for load and store operations, transferring numbers from
the store to the arithmetical unit or back. There were three separate
readers for the three types of cards.

In 1842, the Italian mathematician Menabrea, who had met the travelling
Babbage in Italy, wrote a description of the engine in French, which was
translated into English and extensively annotated by Lady Ada Augusta,
Countess of Lovelace in 1843. She had become interested in the engine
already 10 years earlier, and based on her additions to Menabrea's paper,
she has been described as the first programmer.

In 1878, a committee of the British Association for the Advancement of
Science recommended against constructing the analytical engine.

In 1910, Babbage's son Henry P. Babbage reported that a part of the mill and
the printing apparatus had been constructed and had been used to calculate a
(faulty) list of multiples of Pi. This constituted only a small part of the
whole engine; it was not programmable and had no storage.

The analytical engine was then all but forgotten. However, Howard Hathaway
Aiken, who later constructed the electric automatic calculating machine
Harvard Mark I, was influenced by its design.

From Babbage's autobiography:

     As soon as an Analytical Engine exists, it will necessarily guide the
     future course of the science.

Influences

The cyberpunk novelists William Gibson and Bruce Sterling co-authored a
steampunk novel of alternative history entitled The Difference Engine in
which Babbage's difference and analytical engines became available to
Victorian society. The novel explores the consequences and implications of
the early introduction of computational technology.