Historically, the most important early computing instrument is the abacus, which has been known and widely used for more than 2,000 years. Another computing instrument, the astrolabe, was also in use about 2,000 years ago for navigation.Blaise Pascal is widely credited with building the first "digital calculating machine" in 1642. It performed only additions of numbers entered by means of dials and was intended to help Pascal's father, who was a tax collector. In 1671, Gottfried Wilhelm von Leibniz invented a computer that was built in 1694; it could add and, by successive adding and shifting, multiply. Leibniz invented a special "stepped gear" mechanism for introducing the addend digits, and this mechanism is still in use. The prototypes built by Leibniz and Pascal were not widely used but remained curiosities until more than a century later, when Tomas of Colmar (Charles Xavier Thomas) developed (1820) the first commercially successful mechanical calculator that could add, subtract, multiply, and divide. A succession of improved "desk-top" mechanical calculators by various inventors followed, so that by about 1890 the available built-in operations included accumulation of partial results, storage and reintroduction of past results, and printing of results, each requiring manual initiation. These improvements were made primarily to suit commercial users, with little attention given to the needs of science. BabbageWhile Tomas of Colmar was developing the desktop calculator Charles Babbage initiated a series of very remarkable developments in computers in Cambridge, England. Babbage realized (1812) that many long computations, especially those needed to prepare mathematical tables, consisted of routine operations that were regularly repeated; from this he surmised that it ought to be possible to do these operations automatically. He began to design an automatic mechanical calculating machine, which he called a "difference engine," an...
