# 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 the design till his death in 1871. Because of financial, political and legal issues, the engine was never actually built. Some believe that the technological limitations of the time were a further obstacle to the construction of the machine; others believe that this perspective is not supported by historical reality. In any case, general-purpose computers that were logically comparable to the analytical engine did not come into existence until about 100 years later.

Babbage began by designing and partially 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 instead.

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 to be provided to the machine on punch cards, a method being used at the time to direct mechanical looms. For output, the machine would have a printer, a curve plotter and a bell. The machine would also be able to punch numbers onto cards to be read in later. It employed ordinary base-10 fixed-point arithmetic. There was a store (i.e. a memory) capable of holding 1000 numbers of 50 digits each. An arithmetical unit (the "mill") would be able to perform all four arithmetical operations.

The programming language to be employed was akin to modern day assembly languages. Loops and conditional branching were possible and so the language as conceived would have been Turing-complete. 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, whom Babbage had met whilst travelling in Italy, wrote a description of the engine in French. In 1843, the description was translated into English and extensively annotated by Ada King, Countess of Lovelace, who had become interested in the engine ten years earlier. In recognition of her additions to Menabrea's paper, she has been described as the first computer programmer. The modern computer programming language Ada is named in her honour.

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 with three known exceptions. Percy Ludgate wrote about the engine in 1915 and even designed his own analytical engine (it was drawn up in detail but never built). Ludgate's engine was much smaller than Babbage's of about 8 cubic feet (230 L) and was capable of multiplying two 20-decimal-digit numbers in about 6 seconds. Leonardo Torres y Quevedo and Vannevar Bush also knew of Babbage's work, though the three inventors likely did not know of each other.

Closely related to Babbage's work on the analytical engine was the work of George Stibitz of Bell Laboratories in New York just prior to WWII and Howard Hathaway Aiken at Harvard, during and just after WWII. They both built electromechanical (i.e. relay-and-switch) computers which were closely related to the analytical engine, though neither was (quite) a modern programmable computer. Aiken's machine was largely financed by IBM and was called the Harvard Mark I.

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.

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