Whether you realize it or not, you already know a lot about computers. You've picked up information from commercials and magazine articles, from books and movies, from conversations and correspondence-perhaps even from using your own computer and trying to figure out why it doesn't always work!

Section A provides an overview that's designed to help you start organizing what you know about computers, provide you with a basic understanding of how computers work, and get you up to speed with a basic computer vocabulary.

A COMPUTER IS...

How old is the word "computer"?

The word "Computer has been part of  the English language since 1646, but if you look in a dictionary printed before 1940, you might be surprised to find a computer defined as a person who performs calculations' Prior to 1940, machines designed to perform calculations were referred to as calculators and tabulators, not computers The modern definition and use of the term "computer' emerged in the 1940s, when the first electronic computing devices were developed.

What is a computer?

Most people can formulate a mental picture of a computer, but computers do so many things and come in such a variety of shapes and sizes that it might seem difficult to distill their common characteristics into an all-purpose definition. At its core, a computer is a device that accepts input, processes data, stores data, and produces output, all according to a senes of stored instructions.

Computer input is whatever is typed, submitted. or transmitted to a computer system. Input can be supplied by a person, by the environment, or by another computer. Examples of the kinds of input that a computer can accept include words and symbols in a document, numbers for a calculation, pictures, temperatures from a thermostat audio signals from a microphone, and instructions from a computer program. An input device, such as a keyboard or mouse, gathers input and transforms it into a series of electronic signals for the computer to store and manipulate.

In the context of computing,  data refers to the symbols that represent facts. objects, and ideas Computers manipulate data in many ways, and this manipulation is called processing The series of instructions that tell a computer how to carry out processing tasks is referred to as a computer program. or simply a "program These programs form the software that sets up a computer to do a specific task. Some of the ways that a computer can process data include performing calculations. sorting lists of words or numbers, modifying documents and pictures. and drawing graphs. In a computer, most processing takes place in a component called the central processing unit (CPU), which is sometimes described as the computers "brain.

A computer stores data so that it will be available for processing. Most computers have more than one location for storing data, depending on how the data is being used. Memory is an area of a computer that temporarily holds data waiting to be processed, stored. or output. Storage is the area where data can be left on a permanent basis when it is not immediately needed for processing.

Output is the result produced by a computer. Some examples of computer output include reports. documents, music, graphs. and pictures An output device displays. prints, or transmits the results of processing Figure 1-1 helps you visualize the input. processing, storage, and output activities of a computer.

FIGURE 1-1
A computer can be defined by its acuity to accept input process data store data, and produce output. all according to a set of instructions from a computer program

A computer accepts input from an input device such as a keyboard mouse. scanner or digital camera

Computers produce output on devices such as screens and printers.
Data is processed in the CPU according to instructions that have peen loaded into the computer s memory

A computer uses disks, CDs and DVDs to permanently store data.

What's so significant about a computer's ability to store instructoils?

Take a moment to think about the way you use a simple hand-held calculator to balance your checkbook each month. You're forced to do the calculations in stages. And although you can store data from one stage and use it in the next stage, you cannot store the sequence of formulas-the program-required to balance your checkbook. Every month, therefore. you have to perform a similar set of calculations. The process would be much simpler if your calculator remembered the set of calculations you needed to perform and simply asked you for this month s checkbook entries.

Early computers" were really no more than calculating devices, designed to carry out a specific mathematical task. To use one of these devices for a different task, it was necessary to rewire its circuits -- a fob best left to an engineer. In a modern computer, the idea of a stored program means that a series of instructions for a computing task can be loaded into a computer's memory These instructions can easily be replaced by a different set of instructions when it is time for the computer to perform another task.

The stored program concept allows you to use your computer for one task, such as word processing, and then easily switch to a different type of computing task, such as editing a photo or sending an e-mail message. It is the single most important characteristic that distinguishes a computer from other simpler and less versatile devices, such as calculators and pocket sized electronic dictionaries