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What is an Electronic Computer?

An electronic computer is a device that can accept information, store it, process it, and present the results of the processing in some acceptable form. A most important adjunct to this definition is that a computer is told how to process the information by instructions, which are stored in coded form inside the computer. A computer thus differs radically from a calculator, which can do the same thing that a computer does, except that the instructions are not stored inside the machine. The coded instructions are called a program (modern usage prefers the word routine). We therefore speak of a computer as an internally-stored-program device.

Modern electronic digital computers have many attributes in common. They are usually built in several units, only one of them is a computer or "processor". The other units are control, storage and input-output devices. The modern machine is more often called a computing system. These systems use semiconductors and include magnetic-core and magnetic-tape storage. Almost every digital computer has been found capable of doing more than it was originally designed to do.

Any computer or calculator contains devices for five main functions: input, storage, arithmetic, control and output. Input refers to the process by which information is put into the machine. Output is the process by which the results are moved out of the machine. Storage refers to the mechanism that can retain information during calculation and furnish it as needed to other parts of the machine. The arithmetic unit is that part of the machine, which can carry out one or more of the basic arithmetic operations on the information held in storage. Finally, the control refers to those parts of the machine that dictate the functions to be performed by all the other parts.

In a computer, four of the five functions are, in principle, the same as in a calculator. Most computers are electronic, so that the practical details of these functions are somewhat different. Originally input to the computer was provided by such things as punched cards or punched paper tapes. Storage was provided by a device such as a rotating magnetic drum or by magnetic cores. Arithmetic was carried out by various electronic circuits, as a part of the control function. Output was provided by such devices as punched cards, punched paper tapes, a typewriter, or a printer, which can print a complete line of information at a time. The main difference is that the instructions telling the computer what to do must be placed in storage before the computer proceeds with the solution of a problem. These instructions, which are made up of ordinary decimal digits are placed in the same storage device that holds the data.

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