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# History Of Computers

The first adding machine, a precursor of the digital computer, was devised in 1642 by the French scientist, mathematician, and philosopher Blaise Pascal. This device employed a series of ten-toothed wheels, each tooth representing a digit from 0 to 9. The wheels were connected so that numbers could be added to each other by advancing the wheels by a correct number of teeth. In the 1670s the German philosopher and mathematician Gottfried Wilhelm Leibniz improved on this machine by devising one that could also multiply.

The French inventor Joseph-Marie Jacquard, in designing an automatic loom, used thin, perforated wooden boards to control the weaving of complicated designs. During the 1880s the American statistician Herman Hollerith conceived the idea of using perforated cards, similar to Jacquard's boards, for processing data. Employing a system that passed punched cards over electrical contacts, he was able to compile statistical information for the 1890 United States census.

The Analytical Engine

Also in the 19th century, the British mathematician and inventor Charles Babbage worked out the principles of the modern digital computer. He conceived a number of machines, such as the Difference Engine, that were designed to handle complicated mathematical problems. Many historians consider Babbage and his associate, the mathematician Augusta Ada Byron, Countess of Lovelace, the true pioneers of the modern digital computer. One of Babbage's designs, the Analytical Engine, had many features of a modern computer. It had an input stream in the form of a deck of punched cards, a "store" for saving data, a "mill" for arithmetic operations, and a printer that made a permanent record. Babbage failed to put this idea into practice, though it may well have been technically possible at that date.

Early Computers

Analogue computers began to be built in the late 19th century. Early models calculated by means of rotating shafts and gears. Numerical approximations of equations too difficult to solve in any other way were evaluated with such machines. Lord Kelvin built a mechanical tide predictor that was a specialized analogue computer. During World Wars I and II, mechanical and, later, electrical analogue computing systems were used as torpedo course predictors in submarines and as bombsight controllers in aircraft.

Another system was designed to predict spring floods in the Mississippi River basin.

Electronic Computers

During World War II a team of scientists and mathematicians, working at Bletchley Park, north of London, created one of the first all-electronic digital computers: Colossus. By December 1943, Colossus, which incorporated 1,500 vacuum tubes, was operational. It was used by the team headed by Alan Turing, in the largely successful attempt to crack German radio messages enciphered in the Enigma code.
Independently of this, in the United States, a prototype electronic machine had been built as early as 1939, by John Atanasoff and Clifford Berry at Iowa State College. This prototype and later research were completed quietly and later overshadowed by the development of the Electronic Numerical Integrator And Computer (ENIAC) in 1945. ENIAC was granted a patent, which was overturned decades later, in 1973, when the machine was revealed to have incorporated principles first used in the Atanasoff-Berry Computer (ABC).

ENIAC contained 18,000 vacuum tubes and had a speed of several hundred multiplications per minute, but originally its program was wired into the processor and had to be manually altered. Later machines were built with program storage, based on the ideas of the Hungarian-American mathematician John von Neumann. The instructions, like the data, were stored within a "memory", freeing the computer from the speed limitations of the paper-tape reader during execution and permitting problems to be solved without rewiring the computer. See Von Neumann Architecture.

The use of the transistor in computers in the late 1950s marked the advent of smaller, faster, and more versatile logical elements than were possible with vacuum-tube machines. Because transistors use much less power and have a much longer life, this development alone was responsible for the improved machines called second-generation computers. Components became smaller, as did inter-component spacings, and the system became much less expensive to build.

Integrated Circuits

Late in the 1960s the integrated circuit, or IC, was introduced, making it possible for many transistors to be fabricated on one silicon substrate, with interconnecting wires plated in place. The IC resulted in a further reduction in price, size, and failure rate. The microprocessor became a reality in the mid-1970s with the introduction of the large-scale integrated (LSI) circuit and, later, the very large-scale integrated (VLSI) circuit (microchip), with many thousands of interconnected transistors etched into a single silicon substrate.
To return, then, to the switching capabilities of a modern computer: computers in the 1970s were generally able to handle eight switches at a time.

That is, they could deal with eight binary digits, or bits, of data, at every cycle. A group of eight bits is called a byte, each byte containing 256 possible patterns of ONs and OFFs (or 1s and 0s). Each pattern is the equivalent of an instruction, a part of an instruction, or a particular type of datum, such as a number or a character or a graphics symbol. The pattern 11010010, for example, might be binary data-in this case, the decimal number 210 (see Number Systems)-or it might be an instruction telling the computer to compare data stored in its switches to data stored in a certain memory-chip location.
The development of processors that can handle 16, 32, and 64 bits of data at a time has increased the speed of computers. The complete collection of recognizable patterns-the total list of operations-of which a computer is capable is called its instruction set. Both factors-the number of bits that can be handled at one time, and the size of instruction sets-continue to increase with the ongoing development of modern digital computers.

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