Abacus


Computers truly came into their own as great inventions in the last two decades of the 20th century. But their history stretches back more than 2500 years to the abacus: a simple calculator made from beads and wires, which is still used in some parts of the world today. The difference between an ancient abacus and a modern computer seems vast, but the principle-making repeated calculations more quickly than the human brain-is exactly the same.


Today, most computers are not even recognisable as such: they are embedded in everything from microwave ovens to mobile phones and digital radios.


It is a measure of the brilliance of the abacus, invented in the Middle East circa 500 BC, that it remained the fastest form of calculator until the middle of the 17th century. Then, in 1642, aged only 18, French scientist and philosopher Blaise Pascal (1623-1666) invented the first practical mechanical calculator, the Pascaline, to help his tax collector father do his sums. The machine had a series of interlocking cogs (gear wheels with teeth around their outer edges) that could add and subtract decimal numbers. Several decades later, in 1671, German mathematician and philosopher Gottfried Wilhelm Leibniz (1646-1716) came up with a similar but more advanced machine. Instead of using cogs, it had a "stepped drum" (a cylinder with teeth of increasing length around its edge), an innovation that survived in mechanical calculators for 300 hundred years. The Leibniz machine could do much more than Pascal's: as well as adding and subtracting, it could multiply, divide, and work out square roots. Another pioneering feature was the first memory store or "register".


Apart from developing one of the world's earliest mechanical calculators, Leibniz is remembered for another important contribution to computing: he was the man who invented binary code, a way of representing any decimal number using only the two digits zero and one. Although Leibniz made no use of binary in his own calculator, it set others thinking. A century after Leibniz had died, Englishman George Boole (1815-1864) used the idea to invent a new branch of mathematics called Boolean algebra. In modern computers, binary code and Boolean algebra allow computers to make simple decisions by comparing long strings of zeros and ones. But, in the 18th century, these ideas were still far ahead of their time. It would take almost another 200 years for early computer scientists to work out how to use them.