 | Charles Babbage: Encyclopedia II - Charles Babbage - Design of computers
Charles Babbage - Design of computers
In recognition of the high error rate in the calculation of mathematical tables, Babbage wanted to find a method by which they could be calculated mechanically, removing human sources of error. Three different factors seem to have influenced him: a dislike of untidiness; his experience working on logarithmic tables; and existing work on calculating machines carried out by Wilhelm Schickard, Blaise Pascal, and Gottfried Leibniz. He first discussed the principles of a calculating engine in a letter to Sir Humphrey Davy in 1822.
Babbage's engines were among the first mechanical computers. His engines were not actually completed, largely because of funding problems and personality issues. Babbage realized that a machine could do the work better and more reliably than a human being. Babbage controlled building of some steam-powered machines that more or less did their job; calculations could be mechanized to an extent. Although Babbage's machines were mechanical monsters their basic architecture was astonishingly similar to a modern computer. The data and program memory were separated, operation was instruction based, control unit could make conditional jumps and the machine had a separate I/O unit. Inventions not talked about here but worth mentioning are: The cowcatcher, dynamometer, standard railroad gauge, uniform postal rates, occulting lights for lighthouses, Greenwich Time signals, and heliograph ophthalmoscope.
Charles Babbage - Difference engine
In Babbage’s time numerical tables were calculated by humans called ‘computers’. At Cambridge he saw the high error rate of the people computing the tables and thus started his life’s work in trying to calculate the tables mechanically, removing all human error. He began in 1822 with what he called the difference engine, made to compute values of polynomial functions.
Unlike similar efforts of the time, Babbage's difference engine was created to calculate a series of values automatically. By using the method of finite differences, it was possible to avoid the need for multiplication and division.
The first difference engine needed around 25,000 parts of a combined weight of fifteen tons standing eight feet high. Although he received much funding for the project, he did not complete it. He later designed an improved version, "Difference Engine No. 2". This was not constructed at the time, but was built using his plans in 1989-1991, to 19th century tolerances, and performed its first calculation at the London Science Museum bringing back results to 31 digits, far more than the average modern pocket calculator.
Charles Babbage - Printer
Babbage designed a printer for the second difference engine which had some remarkable features; it supported line-wrapping, variable column and row width, and programmable output formatting.
Charles Babbage - Analytical engine
Soon after the attempt at making the difference engine crumbled, Babbage started designing a different, more complex machine called the Analytical Engine. The engine is not a single physical machine but a succession of designs that he tinkered with until his death in 1871. The main difference between the two engines is that the Analytical Engine could be programmed using punch cards, an idea unheard of in his time. He realized that programs could be put on similar cards so the person had to only create the program initially, and then put the cards in the machine and let it run. The analytical engine was also proposed to use loops of Jacquard's punched cards to control a mechanical calculator, which could formulate results based on the results of preceding computations. This machine was also intended to employ several features subsequently used in modern computers, including sequential control, branching, and looping, and would have been the first mechanical device to be Turing-complete.
Ada Lovelace, an impressive mathematician and one of the few people who totally understood Babbage's vision, created a program for the Analytical Engine. Had the Analytical Engine ever actually been built, her program would have been able to calculate a numerical sequence known as Bernoulli figures. Based on this work, Ada is now credited as being the first computer programmer and, in 1979; a contemporary programming language was named Ada in her honour. Shortly afterward, in 1981, a satirical article in Datamation magazine described the Babbage programming language, the "language of the future".
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 Adapted from the Wikipedia article "Design of computers", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki |
