Early people lived for centuries without keeping any records. Mostly, they used their fingers for counting and keeping records at first but it became difficult and even not sufficient. That calculation was slow, so when the humans faced the problems, they had gradually invented new machines for faster and easier calculation. We can divide the History of the Computer into three eras: the Mechanical Calculating era, Electro-Mechanical era, and Electronic computer era.

## Mechanical Calculating Era

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**Abacus**

The abacus was the earliest counting device invented somewhere in China or Egypt. The Chinese abacus was called 'sun pan' which means counting board. An abacus was made up of a rectangle frame divided into 2 unequal parts called heaven and earth containing several rods and wires. The lower part contains 5 beads and the upper part contains 2 beads in each wire or rod. One can count as well as find the sum and difference by moving the beads. Although the abacus was invented around 600 B.C., peoples of the Far East still use it and can perform calculations at amazing speed.

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**Napier's Bone**

John Napier was a great Scottish mathematician who invented the principle of calculation called the logarithm in 1614 AD. Then he used the same principle for the invention of a small device. That device contained 10 rods carved with numbers and each rod was divided into 9 diagonal numbered parts. That device was called Napier's bone. People used the device for faster multiplication.

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**Slide Rule**

Based on the principle of John Napier, William Oughtered, an English mathematician, invented the machine called Slide Rule in 1620 AD. Slide rule contains 2 rulers carved with numbers and people could use it to perform multiplication and division faster. It performs calculations based on the principles of bones and logarithms. It is the first analog computing device.

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**Pascaline**

Blaise Pascal developed Pascaline in 1642 AD. He was a famous French mathematician and philosopher. He invented the device to help his father in his profession. To perform addition and subtraction, it has cogs and gears rotating in complement to each other respectively. Later to honor him for his contribution to the development of computers, a programming language was given the name "Pascal".

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**Stepped Reckoner**

G.V Leibniz was a German mathematician. He modified the Pascaline and made his own device called Stepped Reckoner in 1671 AD by applying the principle of Pascal. It also had gears to work. It could do addition, subtraction, multiplication, and division and find out square root by a series of stepped additions. Reckoner designed this machine so that its centerpiece was the stepped-drum gear that provides an elongated simple flat gear. This gear principle was employed in many mechanical calculators until they were replaced by electronic calculators in the 1960s.

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**Charles Babbage's Engine (Difference Engine and Analytical Engine)**

Charles Babbage was born in the family home of Teignmouth, Devonshire, the United Kingdom in 1791. His first invention was difference engine and it was powered by steam. In 1822 AD, he requested the British government for financial support to build a machine that would calculate tables for logarithms according to his design. Similar to earlier innovations, Babbage's difference engine was based on a complex system of cogs and levers, powered by steam. It was fully automatic for the mathematical calculation as well as printing out tables. It was controlled by a fixed instruction program that was executed only in a precise linear sequence.

He also designed another machine called Analytical Engine in 1833 AD after
10 years of inventing difference engine but unfortunately, he was unable to
complete it. The analytical engine was an interconnected maze of gears,
cams, and shafts powered by steam. This machine capable of some form of
charges and calculating up to 20 decimals at about 60 additions per minute
could store information, make decisions, and carry out instructions based on
its decisions.

However, Babbage could not finish the analytical engine,
but that principle was used in the development of the basic elements of
modern computers such as input/output, storage, processors, and control
unit. In other words, he discovered the principle for the construction of
general-purpose fully programmable automatic mechanical computer, on which
the modern electronic computers are based. In this way, Peoples considered
Charles Babbage as "father of computer".

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**Lady Augusta Ada**

Ada was the little daughter of extraordinary English poet Lord Byron and an admirer and supporter of Charles Babbage. She suggested Babbage use a binary number system for program and data for the first time. She is the first computer programmer. So, a programming language was named "Ada" to honor her for the contribution to computer programming. Military personnel used "Ada" in the UV defense department for a long time.

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**George Boole**

He is one of the greatest English mathematicians and contributed greatly to the study of symbolic logic during the mid 19th century (the 1950s). He is known for the discovery of 'Boolean Algebra' which is mathematical logic. It was the foundation of modern electronic computer architecture by using 0 or 1 for the electric circuit. Since switching mechanisms at the time could only produce the two actions 'on and off, Boolean algebra provided engineers a medium to communicate with their computers.

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**Tabulating Machine**

Dr. Herman Hollerith invented the tabulating machine. He worked in the Us census bureau. By using the similar ideas of Jacquard's loon, he made the tabulating machine in 1886 AD. It could process on the punch card and perform the census calculation faster. He established his own Tabulating Machine Company (TMC) company, later TMC integrated with other companies and established IBM in 1923 AD. International Business Machine (IBM) is the largest computer manufacturing company in the world even today.

## Electro-Mechanical Era

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**Mark I**

Based on the principle of Charles Babbage, Howard Aiken build up an electro-mechanical computer in 1937 AD. It is also known as IBMASCC (IBM Automatic Sequence Control Calculator). It was designed and built in a complicated way as it contained 7,50,000 parts and was connected with about 500 miles of wires. It was very huge in size as its dimension was 50 feet long, 8 feet high, and 3 feet wide. Its weight was about 32 tons and it had 18,000 vacuum tubes. This computer requires a lot of electricity and delivered substantially more heat.

This computer is controlled by pre-punched paper tape. Due to which it could carry out mathematical operations like addition, subtraction, multiplication, division based on previous results. It had an exceptional subroutine for logarithms and trigonometric functions and used 23 decimal place numbers. It uses an electric typewriter to display all output. By the present guidelines, the Mark I was moderate, requiring 3-5 seconds for a multiplication calculation.

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**Mark II**

Howard Aiken used high-speed electromagnetic relays instead of electromechanical relays for the development of the Mark II, which makes it much faster and convenient than Mark I. A special quality of the Mark II is that it had built-in hardware for some tasks such as the reciprocal, square roots, logarithm, exponential, and some trigonometric functions. There took between five and twelve seconds to execute.

The Mark II was not a stored-program computer - it reads an instruction of the program one at a time from a tape and executes it like the Mark I. It was conveyed to the US Navy Proving Ground at Dahlgren, Virginia in 1947 or 1948.

## Electronic Computers Era

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**ENIAC (Electronic Numerical Integrator And Calculator)**

ENIAC means "Electronic Numerical Integrator And Calculator" which was the first general-purpose electronic computer built in by John William Mauchly and J. Presper Eckert in 1946 AD. It was built to fulfill the requirements of the US armed force. It was 10 feet tall, occupied about 1000 sq. feet, weighing 30 tons, and more than 18,000 vacuum tubes were used. In this way, it also consumes a lot of electricity and delivered substantially more heat. It could do 5,000 addition and 300 multiplication per second.

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**J.V. Neumann**

He was a mathematician. He discovered stored-program technology in 2945 AD.
This turned into the key program innovation for the modern digital
computer.

This technology made computer programming and computing
faster, more flexible, and more efficient. The key element to the central
processing unit, which allowed all computer functions to be coordinated
through a single source. He is renowned as "father of stored program".

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**EDSAC (Electronic Delay Storage Automatic Computer)**

EDSAC stands for electronic delay storage automatic computer which was made by Maurice Wilkes in 1949 AD by applying J.V. Neumann's "stored-program technique". EDSAC contained 3,000 vacuum tubes and utilized mercury delay lines for memory. To input programs, paper tape was used and the teleprinter was used to pass output results. Additionally, EDSAC is credited as utilizing "Initial Orders", which permitted it to be programmed or customized symbolically instead of using machine code.

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**EDVAC (Electronic Discrete Variable Automatic Computer)**

EDVAC represents "Electronic Discrete Variable Automatic Computer" invented
by J.W. Mauchly and J.P. Eckert in 1952 AD. It was also based on J.V.
Neumann's stored-program technique.

It was a binary serial computer
with 1,000 words(44-bit) of ultrasonic serial memory capacity. It could
perform automatic checking and automated addition, subtraction,
multiplication, and programmed division.

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**UNIVAC (UNIVersal Automatic Computer)**

UNIVAC stands for "UNIVersal Automatic Computer". It was the first general-purpose electronic digital computer made for business and administrative use (that is for the fast election of large numbers of relatively simple arithmetic and data transport operations). Before this, the computers were used for the census, calculation, and defense departments only. It was also made by J.W. Mauchly and J.P. Eckert in 1962 AD. It was 8 feet high, 15 feet long and weighed was about 15 tons.

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