Computers

A computer is a machine that receives, stores, manipulates and communicates information¹. It does so by breaking a task down into logical operations² carried out on binary numbers — of O's and l's — and doing hundreds of thousands or millions of such operations per second. At the heart of the computers is³ the central processing unit ⁴,which performs the basic arithmetic and logic functions and supervises the operation of the entire system. In a personal computer the central processing unit is a microprocessor: a single integrated circuit on a chip of silicon that is typically about a quarter of an inch on a side. Other silicon chips constitute the computer's primary memory,where both instructions and data are stored⁵. Still other chips govern the input and output of data and carry out control operations. The chips are mounted on a heavy plastic board; a printed pattern of conductors interconnects the chips and supplies them with power. The board is enclosed in a cabinet; in some instances there are several boards.

Information is entered into the computer by means of a keyboard ⁶or is transferred into it from secondary storage on magnetic tapes or discs. The computer's output is displayed on a screen ⁷,either the computer's own cathode-ray tube,called a monitor, or an ordinary television screen. The output called a modem can be attached to convert the computer's digital signals⁸ into signals for transmission over telephone lines.

The chips and other electronic elements and the various peripheral devices constitute the computer's hardware. The hardware can do nothing by itself; it requires the array of programs, or instructors, collectively called software. The core of the software is an "operating system" that controls the computer's operations and manages the flow of information. The operating system mediates between the machine and the human operator and between the machine and an "application" program that enables the computer to perform a specific task: solving a differential equation ⁹or editing a letter¹⁰.