Necessity is the mother of invention. The saying holds true for computers also, because computers were invented because of man’s search for fast and accurate calculating devices.

The first mechanical adding machine was invented by Blaise Pascal in 1642.Later, in the year 1671; Baron Gottfried Wilhelm von Leibniz of Germany invented the first calculator for multiplication. Keyboard machines originated in the United States around 1880 and are extensively used even today. Around this period only, Herman Hollerith came up with the concept of punched cards, which were extensively used as input medium in computers even in late 1970s, Business machines and calculators made their appearance in Europe and America towards the end of the nineteenth century.

Charles Babbage, a nineteenth century Professor at Cambridge University, is considered the faster of modern digital computers. During his period, mathematical and statistical tables were prepared by a group of clerks. Even the utmost care and precautions could not eliminate human errors. Babbage had to spend several hours checking these tables. Soon he became dissatisfied and exasperated with this type of monotonous job. The result was that he started thinking to build a machine, which could compute tables guaranteed to be error-free. In this process, Babbage designed a “Difference Engine “in the year 1822, which could produce reliable tables. In 1842, Babbage came out with his new idea of Analytical Engine, Which was intended to be completely automatic. It was to be capable of performing the basic arithmetic functions for any mathematical problem, and it was to do so at an average speed of 60 additions per minute. Unfortunately, he was unable to produce a working model of this machine, because the precision engineering required to manufacture the machine was not available during that period. However, his efforts established a number of principles, which have been shown to be fundamental to the design of any digital computer. In order to have better idea of the evolution of computers, let us now briefly discuss about some of the well-known early computers. These are as follows:

1.

**The Mark 1st Computer (1937-44.**Also known as Automatic Sequence Controlled calculator, this was the first fully automatic calculating machine designed by Howard A. Aiken of Harvard University, in collaboration with IBM (International Business Machines).Corporation .Its design was based on the techniques already developed for punched card machinery. It was an electro-mechanical device, since both mechanical and electronic components were used in its design.Although this machine proved to be extremely reliable, It was very complex in design and huge in seize. It used over 3000 electrically actuated switches to control its operations, and was approximately 50 feet long and 9 feet high. It was capable of performing five basic arithmetic operations: addition, subtraction, multiplication, division and table reference. A number as big 23 decimal digits could be used in this machine. It took approximately 0.3 second to add two numbers and 4.5 seconds for multiplication of two members. Hence, the machine was very slow as compared to today’s computers.

2.

**The Atanasoff-Berry Computer (1939-42).**This electronic machine was developed by Dr.John Atanasoff to solve certain mathematical equations. It was called the Atanasoff-Berry Computers, Or ABC,after its inventor’s name and his assistant, Clifford Berry. It used 45 vacuum tubes for internal logic and capacitors for storage.3.

**The ENIC (1943-46).**The Electronic Numerical Integrator and Calculator (ENIAC) was the first all electronic computer. It was constructed at the Moore School of Engineering of the University of Pennsylvania, U.S.A by a design team led by Professor J.Presper Eckert and John Mauchly.ENIC was developed because of military need, and was used for many years to solve ballistic problems, It took up the wall space in a 20*40 square feet room and used 18,000 vacuum tubes, The addition of two numbers was achieved in 200 microseconds, and multiplication in 2000 microseconds.

4.

**The EDVAC (1946-56).**A major drawback of ENIAC was that its program was wired on boards, which made it difficult to change the programs. This problem was later overcome by the “stored program” concept introduced by Dr.John Von Neumann. The basic idea behind this concept is that a sequence of instructions, as well as data, can be stored in the memory of the computers, for automatically directing the flow of operations. This feature considerably influenced the development of modern digital computers because of the ease with which different programs can be loaded and executed on the same computer. Due to this feature, we often refer to modern digital computers as stored program digital computers. The Electronic Discrete Variable Automatic Computer (EDVAC) was designed on stored both instructions and data in the binary form (a system that uses only two digits -0 & 1 to represent all characters), instead of the decimal numbers or human readable words.5.

**The EDSAC (1947-49).**Almost simultaneously with EDVAC of U.S.A, the Bruisers developed the Electronic Deley Storage Automatic Calculator (EDSAC). The machine executed its first program in May 1949.In this machine, addition operation was accomplished in 1500 microseconds, and multiplication operation in 400 microseconds. The machine was developed by a group of scientists, head by Professor Maurice Wilikes, at the Cambridge University Mathematical Laboratory.6.

**The UNIVAC 1**The Universal Automatic Computer (UNIVAC) 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 in 1951 and was used continuously for 10 years. The first business use of a computer, a UNIVAC 1^{st}(1951).^{st}, was by General Electric Corporation in 1954.In 1952, the International Business Machines (IBM) Corporation introduced the 701 commercial computers. In rapid succession, improved models of the UNIVAC 1

^{st}and other 700-series machines were introduced. In 1053, IBM produced the IBM-650, and over 1000 of these computers.The commercially available digital computers, which could be used for business and scientific applications, had arrived.