Thursday, October 15, 2009

Computing - The Difference Engine

In 1790, shortly after the start of the French Revolution, Napoleon Bonaparte decided that the republic required a new set of maps to establish a fair system of property taxation. He also ordered a switch from the old imperial system of measurements to the new metric system. To aid the engineers and mathematicians making the change, the French ordinance survey office commissioned a fresh set of mathematical tables.

In the 18th century, however, computations were done by hand. A “factory floor” of between 60 and 80 human computers added and subtracted numbers to fi ll in line after line of the tables for the survey’s Tables du Cadastre project. It was grunt work, demanding no special skills above basic numeracy and literacy. In fact, most computers were hairdressers who had lost their jobs—aristocratic hairstyles being the sort of thing that could endanger one’s neck in revolutionary France.

The project took about 10 years to complete, but by then the war-torn republic did not have the funds necessary to publish the work. The manuscript languished in the Académie des Sciences weapfor decades. Then, in 1819, a young British mathematican named Charles Babbage would view it on a visit to Paris. Babbage was 28 at the time; three years earlier he had been elected to the Royal Society, the most prominent scientific organization in Britain. He was also very knowledgeable about the world of human computers—at various times he personally supervised the construction of astronomical and actuarial tables.

On his return to England, Babbage decided he would replicate the French project not with human computers but with machinery. England at the time was in the throes of the Industrial Revolution. Jobs that had been done by human or animal labor were falling to the efficiency of the machine. Babbage saw the power of mechanization and realized that it could replace not just muscle but the work of minds. He proposed the construction of his Calculating Engine in 1822 and secured government funding in 1824. For the next decade he immersed himself in the world of manufacturing, seeking the best technologies with which to construct his engine.

The year 1832 was Babbage’s annus mirabilis. That year he not only produced a functioning model of his calculating machine (which he called the Difference Engine) but also published his classic Economy of Machinery and Manufactures, establishing his reputation as the world’s leading industrial economist. He held Saturday evening soirees at his home in Dorset Street in London, which were attended by the front rank of society. At these gatherings the model Difference Engine was placed on display as a conversation piece.

A year later Babbage abandoned the Difference Engine for a grander vision that he called the Analytical Engine. Whereas the Difference Engine had been limited to the single task of table making, the Analytical Engine would be capable of any mathematical calculation. Like a modern computer, it would have a processor that performed arithmetic (the “mill”), memory to hold numbers (the “store”), and the ability to alter its function via user input, in this case by punched cards. In short, it was a computer conceived in Victorian technology.

Babbage’s decision to abandon the unfinished Difference Engine was not well received, however, and the government demurred to supply him with additional funds. Undeterred, he produced thousands of pages of detailed notes and machine drawings in the hope that the government would one day fund construction. It was not until the 1970s, well into the computer age, that scholars studied these papers for the first time. The Analytical Engine was, as one of those scholars remarked, almost like looking at a computer designed on another planet.

Source of Information : Scientific American September 2009

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