# What is a Computer?

Computers are devices that perform calculations and process data. Modern computers are the culmination of a long line of devices used as aids in calculation, including fingers, tallying pebbles, the abacus, and the adding machine.

There are two basic types of computers: analog and digital. Analog computers produce a computation by using operations on continuously variable physical quantities to represent other operations on other physical quantities or on numbers. For example, the slide rule uses the addition and subtraction of lengths to represent the multiplication and division of numbers. There is a wide Variety of analog computers, many of them especially useful in engineering research or design work.

The most powerful type of analog computer, the electronic analog computer, was introduced in the late 1940's. In the electronic analog computer, input data are represented by voltages, resistances, and other electrical quantities. The computer processes information in the form of electrical signals that may be represented as continuous curves; therefore, the results produced are normally continuous curves or meter readings on continuous scales rather than discrete numbers. Such analog computers are able to add, subtract, multiply, divide, and perform more complex mathematical operations.

Digital computers are designed to process discrete numerals, or digits. All digital devices operate by performing one or more of the basic arithmetical operations (addition, subtraction, multiplication, and division) on pairs of numerals. A digital computer can also rearrange numerals or compare two numerals and then take some predetermined action in accordance with what it finds. All of the calculating and data-processing tasks of the computer are performed by repeated applications of a few basic capabilities such as these.

The digital computer functions fundamentally as a numerical transformer of coded information. It takes sets of numerals, processes them as directed by the instructions, and provides another set of numerals as a result. However, almost any information can be translated into a numerical code, and thus into the numerals upon which the computer can operate. Thus, it makes no difference to the computer whether a certain set of numerals represents a vacancy on an airplane, an hour's overtime, a hopper of raw material, or the first line of a Shakespearean sonnet.

The numerals used in digital computers are binary numerals rather than the familiar decimal numerals. In the binary number system, all numbers are expressed by using only two characters, 0 and 1, instead of the 10 characters of the decimal system. Binary numerals have the great advantage of being easily represented by electronic circuits, since an "off" circuit can be used to represent 0 and an "on" circuit to represent 1. This and other characteristics of binary numerals make them particularly suitable for electronic digital computing. See also binary notation.

The great versatility and usefulness of the digital computer are provided by the variety of internally stored programs (or sets of instructions) which guide its operation, by its ability to modify these instructions, and by its capabilities for high-speed operation, storage of large amounts of information, great accuracy, and automatic operation. In fact, its power and utility are so great that the term "computer", when unmodified, has become virtually a synonym for "electronic digital computer."

Computers were developed in the late 1940's, and since then they have had more impact on civilization than any invention since the development of the internal-combustion engine. Almost every modem activity involves the use of a computer, and it is certain that the use of computers will become even more widespread, particularly in the fields of information processing such as education and medicine.

Computers have had their most profound influence on science, business, and industry. Scientific and mathematical research have been vastly accelerated by the use of computers; in business, management practices have been revolutionized by computer methods; and in industry, computers play the vital role of control in automation. Aside from computations made possible by modern digital computers, computers have proved matchless as repositories and correlators of the massive amounts of data generated by an increasing economy and a more complex society.

The number of digital computers in worldwide use increased from less than 15 in 1950 to over 40,000 in the late 1960's with over 100,000 in the 1970's. Together with an increase in numbers has come an increase in the speed capabilities of individual computers. Computers of the late 1960's operated at internal speeds about 20 to 100 times the speeds of their counterparts of 10 years earlier. In addition, the storage capabilities increased eightfold, yet occupied half the former volume.

Now there are computers in millions of homes. In fact often more than one computer. They have become a part of every day life.

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