Charles Babbage is considered to be father of modern computers. He was a professor at Cambridge University. During his time mathematical and statistical tables are made of a group of clerks. Even the out most care can not eliminate the human error in calculations. Babbage had to spend a lot time for checking these tables and soon be become exasperated of doing these types of works. So he started thinking of building a machine which can solve these problems having no error. In the year 1822 he built a Difference computer that can generate reliable tables. In 1842, Babbage came with a new idea of Analytical computer. The Analytical computer was totally automatic and it can perform any type of basic arithmetic at an average speed of 60 additions per minute. But unfortunately he was unable to produce a working model of this computer because precision engineering was not available at that time. However his efforts and principles laid to design the digital computers. We will now discuss about some of the well-known early computers.

- THE MARK I COMPUTER
- THE ATANASOFF-BERRY COMPUTER
- THE ENIAC
- THE EDVAC
- THE EDSAC
- MANCHESTER MARK I
- THE UNIVAC I

## THE MARK I COMPUTER (1937-1944)

The MARK I computer is also known as Automatic Sequence Controlled Calculator was designed by the professor Howard A. Aiken of Harvard University in association with IBM corporation. This computer was the first automatic calculating machine. It was designed based on the punch card machinery which was already developed. This was very huge in size about 50 feet long and 8 feet high. And its design was very complex but this machine proved itself to be extremely reliable. It used over 3000 electrically actuated switches to control its operations. This machine was capable of performing five basic operations as addition, subtraction, multiplication, division and table reference. This machine took around 0.3 second to add two numbers and 4.5 numbers to calculate multiplication of two numbers. Thus this machine was too slow as compared to today’s computers. This computer was an electro – mechanical machine because it was designed with mechanical as well as electrical components. Although its operations were not controlled electronically, Aiken’s machine is often classified as computer because its instructions could be altered.

## THE ATANASOFF-BERRY COMPUTER (1939-1942)

This machine was designed by Dr. John Atanasoff and his assistant Clifford Berry to solve certain mathematical equations. This computer was called Atanasoff-Berry Computer or ABC, after its inventor names. It used 45 vacuum tubes for internal logic and capacitor for storage.

## THE ENIAC (1943-1946)

The ENIAC also known as the Electronic Numerical Integrator And Calculator was the first completely electronic computer. it was designed by the professor J. Presper Eckert and John Mauchly and by their team at the Moore school of engineering of the university of Pennsylvania, United State of America. It was developed for the military. The size of this computer was 20 X 40 square feet and it had 18000 vacuum tubes. It took 200 microsecond (2×10

^{-4}second) to compute addition of two numbers and 2000 microseconds (2×10^{-3}seconds) to find multiplication of two numbers. The ENIAC was much faster than the MARK I computer.### Major Shortcomings of ENIAC:

There are two major shortcomings of this computer. First it could store and manipulate only a small amount of information and second its programs were wired on the boards. These shortcomings made it difficult to find errors and to change the program. Thus its use was limited. Except having these shortcomings it was used for years and it was used to solve ballistic problems.

## THE EDVAC (1946-1952)

The EDVAC also known as Electronic Discrete Variable Automatic Computer was developed by Dr. John Von Neumann. In ENIAC the operation was seriously handicapped by the wiring board but this problem was overcome in this system. EDVAC was based on the concept of stored program. The idea behind stored program was that a sequence of instructions or data can be stored in the memory of the computer for the purpose of automatically flow of operations. Thus the stored program concept influenced for the development of the modern computers which uses the stored program concept. Von Neumann also introduced the idea of storing the information or data in the form of binary number system.

## THE EDSAC (1947-1949)

As the EDVAC was developed in U.S.A. almost in the same time EDSAC was developed in Britain. The EDSAC is known as the Electronic Delay Storage Automatic Calculator. The machine was first started in May 1949. This machine took 1500 microsecond (15×10

^{-4}seconds) to accomplish addition of two numbers. And it took 4000 microsecond (4×10^{-3}second) to accomplish multiplication of two numbers. This machine was developed by Professor Maurice Wilkes and his team at the Cambridge University.## MANCHESTER MARK I (1948)

This computer was a small experiment machine based on the stored program concept. It was designed at the Manchester University by a group of scientists headed by the Professor M.H.A. Newman. Its Storage capacity was only 32 words. This was too limited to store data and instruction. Hence the Manchester Mark I was hardly used.

## THE UNIVAC I (1951)

The UNIVAC is known as Universal Automatic Computer it was the first digital computer which was not one of kind. Many UNIVAC machines were produced, the first of which was installed in the Census Bureau in1951and was used for continuously for 10 years. The first business use of a computer, a UNIVAC I, was by General Electric Corporation in 1954. In 1952 IBM Corporation introduced the 701 commercial computers. The commercially available digital computers that could be used for business and scientific applications had arrived.