Charles Babbage

Charles Babbage, FRS (26 December 1791 – 18 October 1871)[2] was an English mathematician, philosopher, inventor, and mechanical engineer who originated the concept of a programmable computer.[3] Parts of his uncompleted mechanisms are on display in the London Science Museum. In 1991, a perfectly functioning difference engine was constructed from Babbage's original plans. Built to tolerances achievable in the 19th century, the success of the finished engine indicated that Babbage's machine would have worked. Nine years later, the Science Museum completed the printer Babbage had designed for the difference engine, an astonishingly complex device for the 19th century. Considered a "father of the computer",[4] Babbage is credited with inventing the first mechanical computer that eventually led to more complex designs.


Difference engine
Main article: Difference engine
In Babbage’s time, numerical tables were calculated by humans who were called ‘computers’, meaning "one who computes", much as a conductor is "one who conducts". At Cambridge, he saw the high error-rate of this human-driven process and started his life’s work of trying to calculate the tables mechanically. 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 London Science Museum's Difference Engine #2, built from Babbage's design.At the beginning of the 1820s, Babbage worked on a prototype of his first difference engine. Some parts of this prototype still survive in the Museum of the history of science in Oxford[24]. This prototype evolved into the "first difference engine." It remained unfinished and the completed fragment is located at the Museum of Science in London. This first difference engine would have been composed of around 25,000 parts, weighed fifteen tons (13,600 kg), and been 8 ft (2.4 m) tall. Although Babbage received ample funding for the project, it was never completed. He later designed an improved version, "Difference Engine No. 2", which was not constructed until 1989–1991, using Babbage's plans and 19th century manufacturing tolerances. It performed its first calculation at the London Science Museum returning results to 31 digits, far more than the average modern pocket calculator.

Completed models
The London Science Museum has constructed two Difference Engines, according to Babbage's plans for the Difference Engine No 2. One is owned by the museum; the other, owned by technology millionaire Nathan Myhrvold, went on exhibit at the Computer History Museum[25] in Mountain View, California on 10 May 2008.[26] The two models that have been constructed are not replicas; until the assembly of the first Difference Engine No 2 by the London Science Museum, no model of the Difference Engine No 2 existed.


                                  參考資料http://en.wikipedia.org/wiki/Charles_Babbage