1. A Brief History of Computers Introduction to Computer Technology

12. Towards computers: The First Mechanical Calculator None of the devices we have so far looked at are true mechanical calculators…. [ They are really just tools that assist in calculation]

13. Towards computers: The First Mechanical Calculator The Forefathers of the Modern Computer Blaise Pascal (1623-1662) Gottfried Wilhelm von Leibniz (1646-1716) Charles Babbage (1812-1833)

14. Pascal’s Arithmetic Machine Pascal's Arithmetic Machine used a series of gears each with ten teeth. Numbers could be entered and the gear would turn the correct number of teeth. The gear train then supplied a mechanical answer equivalent to the correct arithmetic answer. The machine could only add and subtract, while multiplication and division operations were implemented by performing a series of additions or subtractions. NOTE: In fact the Arithmetic Machine could really only add, because subtractions were performed using complement techniques, in which the number to be subtracted is first converted into its complement, which is then added to the first number. Interestingly enough, modern computers employ similar complement techniques. [Known as 2’s complement mathematics] This gear train system is still used by mechanical odometers

15. Leibniz’s Step Reckoner Leibniz developed Pascal's ideas and, in 1671, introduced the Step Reckoner , a device which, as well as performing additions and subtractions, could multiply, divide, and evaluate square roots by series of stepped additions. Pascal's and Leibniz's devices were the forebears of today's desk-top computers, and derivations of these machines continued to be produced until their electronic equivalents finally became readily available and affordable in the early 1970s. Leibniz also strongly advocated the use of the binary number system , which is fundamental to the operation of modern computers .