Necessity is the mother of invention. The saying holds true for computers also because computers were invented as a result of men's search for fast and accurate calculating devices. The earliest device that qualifies as a digital computer "abacus" also known as "soroban".
This device permits the users to represent numbers by the position of beads on a rack. Simple addition and subtractions can be carried out rapidly and efficiently by positioning the beads appropriately. Although the abacus was invented around 600 B.C., and still used in the Far East and its users can operate and calculate at very amazing speeds.
The first mechanical adding machine was invented by Blaise Pascal in 1642. Later, in the year 1671, Baron Gottfried Wilhelm 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 are extensively used as input media in modern digital computers.
Charles Babbage, a nineteenth century professor at Cambridge University, is considered to be the father of modern digital computer. During his period, mathematical and statistical tables were prepared by a group of clerks. Even the extreme care and precautions could not eliminate human errors. Babbage had to spend several hours checking these tables. Soon he became dissatisfied and annoyed with this type of tedious job. The result was that he started thinking to built a machine which could complete tables guaranteed to be error free. In this process, Babbage designed a "Difference Engine" in the 1822, which could produce reliable tables. His efforts established a number of principle which have been shown to be fundamental to the design of any digital computer.
(1) Mark - I Computer (1937 - 44)
(2) ATANASOFF - Berry Computer (1939 - 42)
(3) EDVAC (1946 - 52)
(4) EDVAC (1946 - 52)
(5) EDSAC (1947 - 49)
(6) Manchester Mark - I (1948)
(7) UNIVAC - I (1951)
(1) Mark - I Computer/Automatic Sequence Controlled Calculator (1937 - 44):
Mark - I, 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 Machine) corporation. Its design was based on the techniques already developed for punched card machinery.
Although this machine proved to be extremely reliable, it was very complex in design and huge in size. It used to over 3,000 electrically activate switches to control its operations and was approximately 50 feet long and 8 feet high. It was capable of performing five basic arithmetic operations: addition, subtraction, multiplication, division and table reference. A number as big as 23 decimals digit could be use in this machine. It took approximately 0.3 seconds to add 2 numbers and 4.5 seconds for multiplication of two numbers. Hence, the machine was very slow as compared to today's computers.
It was basically an electromechanically device since both mechanical and electronic components were used in its design. Although its operations were not controlled electronically, Aiken's machine is often classified as computer because its instruction, which were entered by means of punched paper tape, could be altered.
(2) 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 Computer, or ABC, after its inventor's name and his assistant, Clifford Berry. It used vacuum tubes for internal logic and capacitors for storage.
(3) Electronic Numerical Integrated and Calculator (ENIAC) (1943 - 46):
The electronic numerical Integrator and Calculator (ENIAC) was the first electronic computer. It was constructed at the Moor School of Engineering, University of Pennsylvania, USA by a design team led by professor J. Presper Eckert and John Mauchly.
ENIAC was developed for military needs. 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.
Although much faster in speed as compared to Mark I computer, ENIAC had tow major short comings: it could store and manipulate only a very limited amount of information, and its programs were wired on boards. These limitations made it difficult to detect errors and to change the programs. Hence its use was limited. However, whatever be the shortcomings of ENIAC, it represented an impressive feet of electronic engineering and was used for many years to solve problems.
(4) Electronic Discrete Variable Automatic Computer (EDVAC) (1946 - 52):
The operation of ENIAC was seriously handicapped by the writing board. This problem was later overcome by the new concept of "stored program" developed by Dr. John Von Neumann. The basic idea behind the stored program concept is that a sequence of instructions as well as data can be stored in the memory of the computer for the purpose of automatically directing the flow of operations. The stored program feature considerably influenced the development of modern digital computers and because of this feature we often refer to modern digital computers as stored program digital computers.
The Electronic Discrete Variable Automatic Computer (ENIAC) was designed on stored program concept. Von Neumann has also got a credit for introducing the idea of storing 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) Electronic Delay Storage Automatic Calculator (EDSAC) (1947 - 49):
Almost simultaneously with EDVAC of USA, the Britishers developed the Electronic Delay 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 4000 microseconds. The machine was developed by a group of scientists headed by professor Maurice Wilkes at the Cambridge University.
(6) Manchester Mark - I (1948):
This computer was a small experimental machine based on the stored program concept. It was designed at Manchester University by a group of scientists headed by Professor M.H.A. Newman. Its storage capacity was only 32 words. This was too limited to store data and instructions. This was too limited to store data and instructions. Hence, the Manchester MARK - I was hardly of any practical use.
(7) Universal Automatic Computer UNIVAC - I (1951):
The Universal Automatic Computer (UNIVAC) was the first digital computer which was not "one of the 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 - I, was by General Electric Corporation in 1954.
In 1952, the International Business Machine (IBM) Corporation introduced the 701 commercial computer. In rapid succession, improved models of the UNIVAC - I and other 700 - series machines were introduced. In 1950, IBM produced the IBM - 650 and sold over 1000 of these computers. The commercially available digital computers, which could be used for business and scientific applications, had arrived.