A computer is a machine which is used to compute, or calculate, the answer to a number problem. The word computer is usually applied to electronic machines, which work ay high speeds by controlling the movement of the tiny particles of electricity called electrons.
Mechanical adding machines do their work with gears turned by hand or by electricity. They makelong calculations accurately, but they can work no faster than their operators can feed them with numbers. It was an English mathematician, Charles Babbage, who first realized that a really useful calculating machine would need to store inside itself a list of the sums to be done. It could then complete one sum and go on to the next without waiting for an operator to press buttons or turnhandles. Babbage designed his analytical engine in 1833 but it was never finished, because the engineers of the time could not make the device he needed. About 35 years ago these problems were solved with methods based on electronics.
History of Computers
In 1642, Blaise Pascal developed a machine with gears and cranks that was able to calculate the addition of numbers. In 1822, Charles Babbage worked ona mechanical device, but lacking the resources to build such a device, the construction was never completed. Later, in 1833, he created the first automatic digital computer called an analytical engine. This computer was not completed, primarily because of difficulties in fabrication of precision parts. The sequence of arithmetic operations needed to solve a problem was to be controlled by thereading of punched cards. The next development in automatic computation occurred with the use of punched cards by Herman Hollerith, in 1890, to mechanize U.S. census counts. In 1943, Howard Aiken built the Harvard Mark I computer using mechanical counters from business data-processing machines. Program sequencing was by means of paper tape. At the same time Bell Telephone Laboratories developed arelay computer using punched paper tape for input and for sequence control. The Bell computers represented a landmark in reliability in that they could be left running overnight with no one in attendance. The significant development in analogue computers was the invention of a torque amplifier by Vannevar Bush. In 1955, D.R. Hartree fabricated a differential analyzer from English Erector set parts.In such a device shaft motion represents variables, gears give multiplication or division, and differential gears provide addition and subtraction. Integration is accomplished by having a knife-edged wheel rotating at a variable radius on a circular rotating table. A mechanical interconnection of such devices is the analogue of a system represented by a set of differential equations.
In 1946, theENIAC (Electronic Numerical Integrator and Calculator) was demonstrated at the University of Pennsylvania. This computer was a collection of 20 electronic adding machines. The whole system was designed to integrate the ballistic equations so as to produce firing tables. It was a general purpose computer, on the other hand, capable of executing an arbitrary program. As initially conceived, theprogram was established in the computer by patch-panel wiring around the front of the computer. In 1952, semi-permanent wiring was devised and the card reader was used to run it in a card-sequenced mode.
The next significant step in computer development was the stored-program computer. In this computer the program is loaded into the memory along with the initial data. The device is capable of readinginstructions from memory and executing them in an appropriate sequence. Program logic commands allow the user to put together very complex program structures. The first stored-program computer to run was the EDSAC at Cambridge University in England, in May 1949. Soon thereafter the SEAC and SWAC of the National Bureau of Standards, Whirlwind I at the Massachusetts Institute of Technology, and the...