The history of computers has been divided into three eras. First is the **Mechanical era**, second is the **Electro-Mechanical era** and the third is the **electronic computer era**.

## 1. Mechanical era

#### Abacus:

Abacus is the earliest calculating device. It was developed in China **about 3000 years ago**. It was made up of a wooden frame with beads sliding on wires.

#### Napier’s Bone:

In **1640** AD, a Scottish mathematician named **John Napier**. Napier’s bone can multiply simple multiplications with the help of these devices, John Napier was able to invent an algorithm.

#### Slide Rule:

On the basis of Napier’s bone, English mathematician **William Oughtered** invent a machine for mathematical calculation like addition, subtraction, multiplication with** logarithm table** The machine is very popular among engineering technical persons.

#### Pascaline:

Around **1642** AD, French Mathematician **Blaise Pascal** invented the machine that works on **gears and wheels** for calculations. It could add and subtract very fast and **division and multiplication** too.