Computers are electronic devices that perform calculations in millionths of a second. Unlike other computational aids, such as adding machines, computers must be designed to operate with limited human attention. The comparatively slow reactions of human users would severely reduce the computer's tremendous productivity.
Because computers operate without human intervention, before the computer can be utilized, the calculations to be performed must be completely specified. A set of instructions prepared for the computer is called a program.
The program specifies the computations to be performed on a set of data. Data refers to the values used in the calculations. Data prepared in advance is ready when the program is run. A program may be run with many sets of data.
Different sets of data may require slightly different calculations. For example, in a payroll calculation some employees may have a certain deduction, whereas others may not. In order to permit the program to run with many sets of data, a programmer may specify conditional instructions that indicate actions are to be taken only if the data has certain values.
Programs are usually prepared in a special programming language such as the language called FORTRAN. Its similarity to traditional algebraic notation makes FORTRAN a relatively easy-to-learn programming language.
The text refers to a computer in proper terms as a "general purpose stored program digital computer." By general purpose they mean that the computer can be made to do many different types of tasks. Stored program is referred as a program that is stored in the computer's memory.
By digital computer, the author specifies it is a device that computes with digits (numbers). This is in some sense a misnomer, because digital computers can manipulate letters and symbols as well as numbers. However, digit computers were first used for computing with numbers...