Computer can be classified based on technology evolution into zero, first, second, third, fourth, and fifth generations.The first mechanical calculator developed by blaise pascal acted as a model for the modern computer. Since then many machines were developed which lead the way to modern micro computer.A series of scientific break through by many scientists have contributed to produce this electronic machine called the computer.

** Abacus**: Movable beads on a wooden frame constituted the first known calculating device.The abacus was used by the ancient Greeks and Romans .

**Napier Bones**: In 1614, John Napier, a Scottish mathematician, made a more sophisticated computing machine called the Napier bones. This was a small instrument made of 10 rods on which the multiplication table was engraved. It was made of the strips of ivory bones, and so the name Napier bones. This device enabled multiplication in a fast manner, if one of the numbers was of one digit only. Incidentally, Napier also played a key role in the development of logarithms, which stimulated the invention of slide rule, which substituted the addition of logarithms for multiplication. This was a remarkable invention as it enabled to perform the multiplication and division operations by converting them into simple addition and subtraction operations.

**Slide Rule**: The invention of logarithms influenced the development of another famous invention known as slide rule. In 1620 AD, the first slide rule came into existence. It was jointly devised by two British mathematicians, Edmund Gunter and William Oughtred. It was based on the principle that actual distances 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 two sets of scales that are joined together, with a marginal space between them. This space is enough for the free movement of the slide in the groove of the rule. The suitable alliance of two scales enabled the slide rule to perform multiplication and division by a method of addition and subtraction.

**Pascaline**: A Gear driven machine capable of addition, subtraction, and multiplication, considered as first mechanical calculator, was invented by French mathematician Blaise Pascal in year 1642.

**Stepped Reckoner:** In 1694, Gottfried Wilhem von Leibniz, a German mathematician, extended the Pascal's design to perform multiplication and division and to find square root. This machine is known as Stepped Reckoner. It was the first mass-produced calculating device, which was designed to perform multiplication by repeated additions. Like its predecessor, Leibniz's mechanical multiplier worked by a system of gears and dials. The only problem with this device was that it lacked mechanical precision in its construction and was not very reliable.

** Jacquard's loom**: In 1801, a Frenchman named Joseph Jacquard perfected a Loom that was controlled by the holes in a cardboard punched cards. This machine gave idea about storage.

Difference Engine

**Hollerith's Tabulator**: Herman Hollerith invented the punched-card tabulating machine to process the data collected in the United States' census (see Figure 1.8). This electronic machine was able to read the information on the cards and process it electronically. It consisted of a tabulator, a sorter with compartments electronically controlled by the tabulator's counter and a device used to punch data onto cards. This tabulator could read the presence or absence of holes in the cards by using spring-mounted nails that passed through the holes to make electrical connections. In 1896, Hollerith founded the Tabulating Machine Company, which was later named as IBM (International Business Machines).

** Atanasoff Berry Compute**r: This electronic machine was developed by Dr.john Atanasoff in 1939 to certain mathematical equations. It was called Atanasoff-Berry-Computer or ABC, after its inventor's name and his assistant, Clifford Berry. It used 45 vacuum tubes for internal logic and capacitors for storage.

**ABC Computer**: In 1939, John Vincent Atansoft and Clifford Berry formulated the idea of using the binary number system to simplify the construction of an electronic calculator. At the end of 1939, they built the first electronic computer named as ABC (Atansoft Berry Computer). It is considered the first computing machine, which introduced the idea of binary arithmetic, regenerative memory and logic circuits. This computer used electronic vacuum tubes and the circuitry was based on George Boole's Boolean algebra.

**Colossus**: In 1944, Alan Mathison, a British mathematician, along with some colleagues, created a computer called the colossus, which comprised 1800 vacuum tubes. It was one of the world's earliest working programmable electronic digital computers. Colossus was a special-purpose machine that suited a narrow range of tasks (e.g. it was not capable of performing decimal multiplications). Although colossus was built as a special-purpose computer, it proved flexible enough to be programmed to execute a variety of routines.

**ENIAC**: First fully electronic computer named ENIAC(Electronic Numerical Integrator and Calculator) was developed by Prosper Eckert and J.W.Mauchly in 1945.It used high speed vacuum tube switching devices.

**EDVAC**: In 1946, Dr.John Von Neumann used the principle of storing in 0 and 1(Binary Digits) in place of earlier technologies and developed EDVAC with the new concept of stored program.EDVAC (Electronic Discrete Variable Automatic Computer).

** UNIVAC**: Universal Automatic Computer was developed by ECKERT ans MAUCHLY in year 1951.It was the first commercial computer used by Electronic Corporation.Its memory was of MDL(Mercury Delay Line)

PDP Series

- PDP-1 1961 8 bit 4KB
- PDP-8 1965 16 bit 16KB

- PDP-11 1970 16 bit 32KB

**Micro Computer**: Intel is the No.1 company in micro processor.The microprocessor developed by this company were the best for micro computers,few of them are follows:

Model Year Bits

8080 1974 8 bits

8085 1978 8 bits

8086 1980 16 bits

80286 1982 32 bits

80386 1985 32 bits

80486 1956 32 bits

**Pentium Series**: After 80846, Intel developed Pentium processors which are used almost in every computer now a days.

- Pentium 1993
- Pentium 1 1995

- Pentium 2 1997

- Pentium Mobile 1998

- Pentium 3 1999

- Pentium 4 2000

- Pentium Centrino 2004