# Computer Science XI

## Early History

2500 BC – The Abacus
Abacus is the first known calculating machine used for counting. It is made of beads strung on cords and is used for simple arithmetic calculations. The cords correspond to positions of decimal digits. The beads represent digits. Numbers are represented by beads close to the crossbar. Abacus was mainly used for addition and subtraction and later for division and multiplication.

The Napier’s Bones was invented by John Napier, a Scottish mathematician as an aid to multiplication. A set of bones consisted of nine rods, one for each digit 1 through 9 and a constant rod for the digit ‘0’. A rod is similar to one column of a multiplication table.

1633 AD – The Slide Rule
The Slide Rule was invented by William Oughtred. It is based on the principle that actual distance from the starting point of the rule is directly proportional to the logarithm of the numbers printed on the rule. The slide rule is embodied by the two sets of scales that are joined together, with a marginal space between them. The suitable alliance of two scales enabled the slide rule to perform multiplication and division by a method of addition and subtraction.

1642 AD – The Rotating Wheel Calculator
The Rotating Wheel Calculator The Rotating Wheel Calculator was developed by a French philosopher, Blaise Pascal, using simple components such as gears and levers. This is a predecessor to today’s electronic calculator. He was inspired by the computation work of his father’s job and devised the model. He was only 19 years old, when he devised this model.

1822 AD – The Difference Engine
The Difference Engine was built by Charles Babbage, British mathematician and engineer which mechanically calculated mathematical tables. Babbage is called the father of today’s computer.

1890 AD - Hollerith Tabulating Machine
A tabulating machine using punched cards was designed by Herman. Hollerith and was called as the Hollerith Tabulating Machine. This electronic machine is able to read the information on the punched cards and process it electronically. 