Computers DO 'byte'

If you get bored of reading then you might want to check this practical page on computers (PC's).

COMPUTER is a machine that performs calculations and processses information with astonishing speed and precision.  A computer can handle vast amounts of information and solve complicated problems.  It can take thousands of individual pieces of data and turn them into more usable information--with blinding speed and almost unfailing accuracy.  The most powerful computers can perform billions of calculations per second.

Computers handle many tasks in business, education, manufacturing, transportation, and other fields.  They provide scientists and other researchers with a clearer understanding of nature.  They give people who work with words an effective way to create documents.  They enable designers and artists to see things that have never been seen before.  Computers produce new information so quickly and accurately that they are changing people's views of the world.  For these and other reasons, the computer is one of the most interesting and important machines ever invented.

The most common type of computer, by far, is the digital computer.  Digital means having to do with numbers.  Digital computers perform tasks by changing one set of numbers into another set.  All data--numerals, pictures, sounds, symbols, and words--are translated into numbers inside the computer.  Everything a digital computer can do is based on its ability to perform simple procedures on numbers--such as adding, subtracting, or comparing two numbers to see which is larger.  Digital computers are so widespread that the word computer alone almost always refers to a digital computer.  The largest digital computers are parts of computer systems that fill a large room.  The smallest digital computers--some so tiny they can pass through the eye of a needle--are found inside wrist watches, pocket calculators, and other devices.

All digital computers have two basic parts--a memory and a processor.  The memory receives data and holds them until needed.  The memory is made up of a huge collection of switches.  The processor changes data into useful information by converting numbers into other numbers.  It reads numbers from the memory, performs basic arithmetic calculations such as addition or subtraction, and puts the answer back into the memory.  The processor performs this activity over and over until the desired result is achieved.  Both the memory and the processor are electronic--that is, they work by sending electrical signals through wires.

The smallest digital computers consist only of the memory and the processor.  But larger digital computers are part of systems that also contain input equipment and output equipment.  The operator uses an input device, such as a keyboard, to enter instructions and data into the computer.  After processing is complete, an output device translates the processed data into a form understandable to the user--words or pictures, for example.  Typical output devices include printers and visual displays that resemble television screens.

People can think about problems and figure out how to solve them.  But computers cannot think.  A person must tell the computer in very simple terms exactly what to do with the data it receives.  A list of instructions for a computer to follow is called a program.

People have used calculating devices since ancient times.  The first electronic digital computer, built in 1946, filled a huge room.  Since then, rapid improvements in computer technology have led to the development of smaller, more powerful, and less expensive computers.

In addition to digital computers, there are two other general types of computers: analog computers and hybrid computers.  Analog computers work directly with a physical quantity, such as weight or speed, rather than with digits that represent the quantity.  Such computers solve problems by measuring a quantity, such as temperature, in terms of another quantity, such as the length of a thin line of liquid in a thermometer.  Hybrid computers combine the features of analog and digital computers.  They have many of the same kinds of parts as an analog computer.  But like digital computers, they process data by manipulating numbers.  This article focuses on digital computers.  For information on analog computers..

The Importance of the Computer

Computers are tremendously important in a variety of ways.  For example, they simplify many difficult or time-consuming tasks to an extraordinary degree.  They provide businesses, governments, individuals, and institutions with an efficient way to manage large amounts of information.  Computers also help people to understand things better by allowing them to make models and test theories.

The value of computers lies in their ability to perform certain basic tasks extremely quickly and accurately.  These tasks include (1) solving numerical problems, (2) storing and retrieving information, and (3) creating and displaying documents and pictures.

Solving Numerical Problems.  One of the most important and most difficult jobs performed by computers is the solution of complicated problems involving numbers.  Computers can solve such problems amazingly quickly.  In many cases, the solutions show how certain things work, behave, or happen.

In Engineering and the Sciences, the knowledge of how something works is often expressed in the form of an equation.  An equation is a two-part mathematical sentence in which the parts are equal to each other.  Engineers and scientists use equations or groups of equations to show how various things relate to one another.  They use the solutions to these equations to predict what will happen if certain elements of a situation or an experiment are changed.  Engineers and scientists rely on computers to solve the complicated sets of equations that they use to make predictions.

For example, with the help of a computer, an engineer can predict how well an airplane will fly.  A large, complex set of equations expresses the relationships between the various parts of an airplane and what happens when the airplane flies.  The engineer enters the numbers for the size and weight of a certain airplane's parts.  The computer then solves the equations for this particular airplane.  Based on the solutions, the engineer can predict how well the plane will fly.  The engineer then might decide to change the size or weight of one of the airplane's parts to change the way it flies.  Thus, the computer helps the engineer simulate (imitate) various conditions.

Computers help people develop and test scientific theories.  A theory is a proposed explanation for how or why something happens.  Theories, like known relationships, are often expressed as equations.  Some equations are so complicated or time-consuming to solve that it would be impossible to develop the theory without the help of computers.  Computers are particularly useful in developing and evaluating theories about things that are difficult to observe and measure.

For example, an astronomer can use the problem-solving ability of computers to develop theories about how galaxies are formed.  First, the astronomer proposes a set of equations about a group of stars.  A computer performs the calculations needed to solve the equations.  The astronomer can then use the solutions to predict the shape of the galaxy that the stars should form if the theory is correct.  To test the theory, the astronomer can observe a real galaxy to see if it has the predicted shape.

In Economics and Finance, computers solve equations to make predictions about money.  Many of the equations that economists and business people use to make long-range predictions are extremely complicated.  But some of the most widely used of all computer programs rely on fairly simple equations.  Such programs help people and businesses figure out their taxes, create budgets, and calculate the value of their investments.

Storing and Retrieving Information.  People use computers to store unbelievably large quantities of information.  Information stored in a computer is sometimes called a database.  Databases can be enormous--for example, a nation's entire census might be contained in a single database.  A computer can search a huge database quickly to find a specific piece of information.  In addition, the information can be changed easily and quickly--often in less than a second.

The efficiency with which computers store and retrieve information makes them valuable in a wide range of professions.  For example, scientists use computers to store and quickly find results of experiments.  Libraries use computer catalogs to hold information about their collections.  Hospitals use computers to maintain records about their patients.  Governments store election returns and census information on computers.

All kinds of businesses rely on computers to store large quantities of information about their employees, customers, and products.  Computers also allow markets for stocks, bonds, currency, and other investments to keep track of current prices around the world.  Banks maintain many kinds of records on computers, such as account balances and credit card information.  Anyone who uses an automatic teller machine (ATM) is using a computer terminal.  When an identification card and number are entered, the ATM can provide account information, dispense cash, and transfer funds between accounts.

Creating and Displaying Documents and Pictures.  Computers can store a huge number of words in a way that makes it easy to manipulate them.  For this reason, word processing is one of the most important and widespread uses of computers.  A word-processing program allows people to type words into a computer to write articles, books, letters, reports, and other documents.

Word-processing programs make it easy for people to change text that has been typed into a computer.  For example, they can quickly correct typing or spelling errors.  Words, sentences, and entire sections of a document can be added, removed, or rearranged.  If a computer is connected to a printer, the document may be printed at the touch of a key.  Business people, journalists, scientists, secretaries, and students are among those who benefit from word-processing programs.

Computers are also important in the publishing industry.  For example, most books, magazines, and newspapers are typeset by computers.  In addition, a process known as desktop publishing enables people to design newsletters and other documents on personal computers.  Documents that have been created in this manner look as good as or better than those produced in the traditional way.

Computer graphics--the use of computers to make pictures--make up one of the most fascinating and fastest-growing areas of computer use.  Computers can produce pictures that look almost like photographs.  First, the computer solves equations that predict how an object should look.  It then uses these predictions to display a picture on a computer terminal screen or to print a picture on paper.

Computer programs that perform computer-aided design (CAD) are important in many fields, particularly engineering and architecture.  CAD programs create pictures or diagrams of a new object.  The programs then solve equations to predict how the object will work.  Engineers and architects use CAD programs to design airplanes, bridges, buildings, cars, electronic machinery, in addition to many other types of machines and structures.

In addition, computers can produce pictures by converting information into pictorial form.  The pictures can serve a variety of purposes.  For example, computers enable business people, economists, and scientists to plot graphs from lists of numbers.  In a technique called computerized tomography, or the CT scan, a computer uses X-ray data to construct an image of a body part on a screen.  Doctors use these images to help diagnose diseases and disorders.

Computer graphics also are used to create electronic video games.  Terminal monitors or TV screens can display game boards and moving pictures.  The player may use a keyboard or some other device, such as a mouse or a joystick, to play computer games.

Computer designers are experimenting with using computer graphics to create virtual reality--an artificial world in which the computer user can seemingly move about and handle objects.  One virtual reality system has a headset with two tiny display screens, one screen for each eye.  Images on the screens produce a three-dimensional view.  Sensing devices contained in a special glove tell the computer when the user moves the fingers or hand.  The computer then changes the images to create the illusion of, for example, opening a door.

The images do not have nearly the detail of what is seen in the actual world.  In addition, there is a delay between hand movements and the corresponding changes in the images.  But virtual reality has a variety of applications.  These applications range from simple game sets to sophisticated equipment used to control robots.

Other Uses.  Many complex machines need frequent adjustments to work efficiently.  Small computers can be installed inside these machines and programmed to make these adjustments.  In modern automobiles, such embedded (enclosed) computers control certain aspects of operation, such as the mixture of fuel and air entering the engine.  Today's commercial airliners and military planes carry computers that help control the aircraft.  Embedded computers also control the movements of industrial robots and guide modern weapons systems, such as missiles and field artillery, to their targets.

Computers can help solve many complicated problems that do not involve numerical equations.  Doctors, for example, investigate illnesses, decide on diagnoses, and prescribe treatments.  They solve such problems by applying their knowledge and experience, not by solving equations.  A branch of computer science called artificial intelligence uses programs that help solve problems by applying human knowledge and experience.  Artificial intelligence systems called expert systems enable computers programmed with vast amounts of data to "think" about numerous possibilities--such as diseases that certain symptoms could indicate--and make a decision or diagnosis.

Computers also can be used to communicate information over long distances.  They can send information to each other over telephone lines.  As a result, computers keep banks, newspapers, and other institutions supplied with up-to-the-minute information.  A computer network consists of many computers in separate rooms, buildings, cities, or countries, all connected together.  Computer networks allow people to communicate by using electronic mail--a document typed into one computer and "delivered" to another.  Such documents generally travel in only a few seconds, even if they are being sent over a long distance.

Computers also are used in teaching.  Programs that perform computer-aided instruction (CAI) are designed to help students at all levels, from elementary school through the university level.  The student sits at a computer terminal.  The terminal's screen displays a question for the student to answer.  If the answer is wrong or incomplete, the computer may ask the student to try again.  It then may supply the correct answer and an explanation.  CAI also is used in some adult education programs and as part of the employee-training programs of some corporations.

Basic Principles of Computers

A computer receives individual pieces of data, changes the data into more useful information, and then tells the operator what the information is.  For example, a person who wants to find the sum of four numbers enters them into the computer.  In only a fraction of a second, signals that represent these numbers are changed into signals that represent the sum.  The computer then displays the sum for the user.

How a Computer Operates.  People use input devices to enter data into computers.  One of the most common input devices is the computer terminal, which looks like a typewriter keyboard combined with a television screen.  Data that are typed on the keyboard appear on the screen.  At the same time, the data go to the memory.  The memory also stores a program--the step-by-step instructions for the computer to follow.  The processor manipulates the data according to the program.

The processed information is sent to an output device, which presents it to the computer user.  In many cases, the computer terminal that served as the input device also acts as the output device, and its screen displays the results.  Printers are another important kind of output device.  File storage devices are used to save information and programs for future use.

All data handled by computers, including words, enter the processor in the form of digits.  Computers commonly use the digits of the binary numeration system  [The Binary System].  Un like the familiar decimal system, which uses 10 digits, the binary system uses only two digits: 0 and 1.  These digits are called bits.  Different combinations of bits represent letters, symbols, and decimal numerals.  Each such combination of bits is called a byte.  For example, according to one standard code, the binary representation for the letter A is 100 0001, while the binary representation for the letter Z is 101 1010.  Each symbol and decimal numeral also is represented by a specific combination of 0's and 1's.

Each of a computer's thousands or millions of tiny electronic circuits operates much like an ordinary light switch.  When a circuit is off, it corresponds to the binary digit 0.  When a circuit is on, it corresponds to the digit 1.  Binary digits, like decimal numbers, can be added, subtracted, multiplied, and divided.  Thus, a computer can perform all the basic arithmetic operations.

Computer Hardware and Software.  The physical equipment that makes up a computer system is called hardware.  Hardware includes input and output devices, file storage devices, the memory, and the processor.  The input and output devices and the file storage devices also are known as peripheral equipment.

Computer software consists of the programs that a computer uses to perform a task.  People can either create or purchase software.  Computers have vast and varied capabilities because of the many different kinds of available software.

Kinds of Computers

Computers vary widely in size, speed, and ability.  The size of a computer partly determines the kinds and number of jobs it can do.  But even a small computer can perform complicated tasks.  For example, a modern desktop computer has more computing power than the huge, room-filling computers of the early 1960's.

The microprocessor plays an important role in almost all modern computers.  A microprocessor is an electronic device consisting of thousands, or even millions, of transistors and related circuitry on a chip, usually of silicon.  Microprocessors are as small as a fingernail, yet have the computing power of much larger computers built before microprocessors were developed.  Moreover, a microprocessor generally costs much less than would comparable equipment made up of many components.

Digital computers may be grouped into three categories: (1) embedded computers, (2) personal computers and workstations, and (3) mainframes.  The borders between these categories change constantly as smaller, more powerful computers are developed.

Embedded Computers control the operation of various types of machinery.  Virtually all embedded computers are microprocessors.  Such machines as automobiles, digital wrist watches, telephones, and videotape recorders contain embedded computers.

Personal Computers and Workstations are computers used by one person at a time.  Such a computer usually fits on a desk top.  Smaller, portable models are popular with people who often work away from their desks.  Popular portables include laptop computers, which can be held on the lap; notebook computers, which are about the size of a looseleaf notebook; and palmtop, or handheld, computers, which can be operated while held in the hand.  People commonly use personal computers for such activities as word processing, storing and updating information, performing simple calculations, and playing computer games.  These computers also are valuable to business people, who use them to manage information about their inventories, customers, and employees.

Personal computers contain one or more microprocessors.  By modern standards of computer speed and capacity, personal computers execute programs slowly and have limited memory and file storage capacity.

Workstations are more powerful than personal computers, and better suited to solving difficult engineering, graphics, or scientific problems.  Workstations are generally connected to form computer networks.  These networks allow operators to exchange information very rapidly.  They also enable printers and file storage devices to be shared by many workstations.  One important type of computer network, the local area network (LAN), connects workstations located within the same building or in neighboring buildings.  A wide area network (WAN) links workstations over large areas.

Mainframes are fast computers with large memories and file storage systems.  These powerful computers solve very complicated problems and manage huge quantities of information.  Most mainframes are housed in several large cabinets.  Some mainframes do a single job, such as copying and storing the information generated by a laboratory experiment.  Others perform many different tasks.  Minicomputers and superminis have many of the capabilities of mainframes, but they are smaller and less expensive.

On a large mainframe, hundreds of people may be logged on (running programs) at one time.  The use of a single powerful computer by many users at once is called time-sharing.  The mainframe appears to run many programs at the same time.  However, the computer actually switches rapidly from program to program, doing a bit of work on one and then hurrying on to another.

The fastest mainframes are called supercomputers.  Supercomputers solve numerical problems as quickly as possible based on existing technology.  They are used to model weather systems, to design cars and aircraft, and in many other ways.  But supercomputers are rare, because they are extremely expensive.  Individual supercomputer users--mostly scientists and engineers at large scientific installations--sometimes run programs by means of long-distance computer networks.

Mainframes known as parallel computers have provided great increases in speed over other computers.  Most computers have a single processor.  But a parallel computer has many processors that all operate at once.  Each processor can work on a separate piece of a program.  As a result, the program can be run much more quickly than on a computer with only one processor.  The fastest supercomputers in the world are parallel computers.  But parallel computers may even serve as especially fast workstations.

How a Computer Works

Computers can perform many different activities because they can store huge lists of numbers and do arithmetic very rapidly.  All computers work essentially the same way.  A computer encodes (translates) numbers, words, pictures, sounds, and other forms of data into the 0's and 1's of the binary numeration system.  The computer's processor manipulates the binary numbers according to specified instructions.  All changes of the data are accomplished by performing arithmetical calculations on these binary numbers.  Thus, the binary numbers that represent the data are changed into binary numbers that represent the desired information.  The results are decoded (translated back) from binary into decimal numbers, words, pictures, or some other form.

The operation of a computer can be broken down into three steps.  They are (1) entering and encoding data and instructions, (2) processing data, and (3) decoding the results and producing output.  The storing of information occurs during all three steps of the process.

Entering and Encoding Data and Instructions is performed using input equipment.  This section explains how the computer encodes data entered through a terminal.  It also describes a number of other input devices.

Terminals enable computer users to type characters (letters and numerals) directly into the computer.  A terminal includes a keyboard unit and a monitor.  The monitor usually consists of a cathode-ray tube (CRT).  A CRT is a vacuum tube with a screen like that of a television.  The CRT display makes it possible for the user to check the data being entered into the computer and to make corrections if necessary.

As each character is typed, the circuitry inside the terminal puts the character's binary code into a temporary storage location called a buffer.  As soon as a code appears in the buffer, the processor executes an instruction that moves it from the buffer to the computer's memory.  The monitor also has a buffer.  Whenever the processor sends a code into this buffer, the corresponding character appears on the screen.

Other input devices are also used with monitors.  For example, some terminals enable users to communicate with the computer by drawing pictures or diagrams directly on the screen with a light pen.  Such units encode drawings directly from the monitor.  Pen-based computers recognize hand printing and other marks made on the computer screen with an electronic pen.  These light-weight, portable machines can be used to record data in situations where typing would be difficult.

A device called a mouse can be used to give commands to a computer.  When this handheld box is moved on a flat surface, it causes a pointer to point at a specific instruction or piece of data on the monitor.  With many software programs, the instruction appears as an icon (picture) rather than words.  Clicking a button on the mouse causes the instruction to be carried out or the data to be moved or changed.  The ability to give commands to a computer by selecting icons rather than by typing words is known as graphical user interface.

Modems are devices that allow computers to communicate with other computers by using telephone lines.  A modem translates sounds into tones that represent binary numbers.  It can send the tones over the phone lines to other modems.

Modems and telecommunications software make it possible to communicate with computer users throughout the world.  The communication may take place directly, from one computer to another, or by way of an on-line service.  On-line services provide dozens of electronic "meeting rooms" where individuals can discuss shared interests.  The services also offer many other features, including news and weather bulletins, financial advice, shop-at-home services, and computer games.  Most on-line services charge a fee based on how much time customers spend using the service.

Less elaborate than on-line services are computer bulletin board services, known as BBS's.  Computer users can call a BBS and "post" announcements or messages on the electronic "bulletin board," where they can be read by other computer users.

Disk Drives and Tape Drives perform many functions in the operation of the computer.  One of these functions is providing input in binary form.  A disk drive is a machine that, among other things, reads 0's and 1's that are magnetically encoded onto disks.  This information then goes to the buffer and the memory.  A disk system provides quick and direct access to information anywhere on a disk.  Flexible magnetic disks called floppy disks or diskettes are widely used to provide input to personal computers.  Hard disks are used with larger computer systems, as well as with some personal computers.

Tape drives and magnetic tapes work in much the same way.  However, a tape must be unwound or rewound to the location that contains the desired information.  As a result, it takes longer to read information from a tape than from a disk.

Optical Scanners also read data and instructions.  Some scanners optically sense bar codes and other marks that have been printed on identification and credit cards, grocery items, or documents.  They then change these codes into electrical signals.  Other scanners read information from compact discs or optical disks.  Such disks contain digitally encoded data that can be read by a laser beam.

Other Input Devices include a joystick for moving figures about on a screen and a graphic tablet consisting of a pad and a special pen for producing illustrations.  Such devices are used with some personal computers.  Voice activators enable computers to understand spoken words.  Some mainframes obtain input by means of card readers, which take information from punched cards.  The pattern of punches represents letters, numbers, and other symbols.  Card readers once were popular, but today they are used less frequently.

Processing Data.  The processor, also called the central processing unit or CPU, is the heart of the computer.  It manipulates the binary numbers that represent input according to a program, and converts them into binary numbers that represent the desired result.

Since the development of the integrated circuit in the 1960's, the processor in many computers is contained on a single microprocessor--a chip no larger than a fingernail.  All the devices and wires that make up the processor are packed onto the surface of the chip.  The chip is made of a semiconductor material, usually silicon.  The chip's circuitry contains many tiny devices called transistors.  A transistor can either stop electric current or allow it to flow .  A computer processor consists of two parts: (1) the control unit and (2) the digital logic unit.

The Control Unit directs and coordinates the operations of the entire computer according to instructions stored in the memory.  The control unit must select the instructions in proper order because their sequence determines each step in the operations.  Each set of instructions is expressed through a binary operation code that specifies exactly what must be done to complete a job.  The operation code also provides information that tells where data for the processing operation are stored in the memory.  The control unit interprets the instructions and relays commands to the logic unit.  It also regulates the flow of data between the memory and the logic unit and routes processed information to output or file storage devices.

The Digital Logic Unit, sometimes known as the arithmetic/logic unit or ALU, manipulates data received from the memory.  It carries out all the functions and logic processes required to solve a problem.  Computers use logic to perform arithmetical calculations--addition, subtraction, multiplication, and division.

In the digital logic unit, electronic circuits called registers temporarily store data from the memory.  The data consist of electrical signals that represent binary digits.  An electrical signal that has a low voltage level represents 0, and a signal that has a high voltage level represents 1.

To carry out an arithmetical calculation, the electrical signal for each input travels on a wire to another circuit.  The answer comes out on a wire from the other end of the circuit.  There are a number of basic circuits.  Three such circuits are the AND-gate, the OR-gate, and the NOT-gate or inverter.  The basic circuits are combined in different ways to perform arithmetic and logic operations with electrical signals that represent binary digits.  For example, one combination of logic circuits performs addition.  Another combination compares two numbers and then acts on the result of the comparison.

After an operation has been completed, the result may be sent to the memory for storage until it is needed for another operation.  In many cases, the result is sent to an output device or a file storage device.

Decoding the Results and Producing Output.  People use output equipment to get information from computers.  Output equipment translates the electrical signals that represent binary numbers into a form that the user can understand.  Often, the equipment also serves as input equipment.  There are many types of output devices, such as terminals, printers, modems, and disk and tape drives.

Terminals, in addition to serving as input equipment, display output on the monitor.  As information travels from the processor to the terminal, it moves through the buffer that was used in the input function.  On a terminal, a user can receive data in the form of words, numbers, graphs, or pictures.

Printers produce output on paper.  Like terminals, printers have buffers.  To print a character, the processor puts the binary code for that character into the printer's buffer.  The printer prints the character that corresponds to the code.  Some printers operate much like typewriters.  Others use heat, special chemicals, lasers, or combinations of these methods to place characters on paper.

Modems, which translate sounds into binary numbers during the input function, can also provide output by translating binary numbers into sounds.  As a result, they enable users to receive information from distant computers.

Disk Drives and Tape Drives also serve as both input and output equipment.  Magnetic disks and tapes receive output in binary form.  The drives interpret binary information from disks and tapes and present it to the user, often on a monitor.  Output data presented on disks and tapes can easily be put back in the computer when needed.

Other Output Devices include plotters, key punch machines, and audio devices.  Plotters use pens to create drawings, diagrams, and graphs on paper or clear plastic.  Key punch machines record data by punching holes in cards or paper tape.  Audio devices produce spoken words through a type of telephone or loudspeaker.  Audio devices are becoming increasingly important.

Storing Information.  Computers can store information in two types of locations during the computing process--the memory and file storage devices.  Memory, which is built into the computer, holds instructions and data during processing.  File storage devices provide long-term storage of large amounts of information.

Memory, also called the internal memory or main memory, stores information and programs inside the computer.  The memory receives data and instructions from an input device or a file storage device.  It also receives information from the processor.  The memory stores only the information that is currently needed by the processor.  After the processor has finished with it, the information is transferred to file storage devices for permanent storage or sent directly to an output device for immediate use.

The devices and wires that make up the memory can be built from integrated circuits that fit onto one or more chips.  The circuits, wires, and transistors form many memory cells capable of storing binary digits.  These cells are arranged into groups.  Each group is assigned an address--a number that makes it possible to locate specific pieces of information quickly.

File Storage Devices, also called auxiliary storage units, can store huge amounts of information for long periods of time.  Such units are slower than the memory that is built into the computer.  But they can hold much more information, and they are less expensive.  For this reason, file storage devices are commonly used to store large quantities of data, programs, and processed information.

The most important file storage devices are magnetic disks and magnetic tapes.  Disks and tapes are operated by disk drives and tape drives, which also serve as input and output equipment.  These units encode data onto the surfaces of disks and tapes by turning the electrical signals that represent the 0's and 1's of binary code into magnetism.  Every 0 is represented on the disk or tape by a little magnet pointing in a certain direction, and every 1 by a magnet pointing in the opposite direction.  To read information from a disk or tape, the drive unit translates the magnetic signals into electrical signals and sends them to the memory.  Magnetic disks and tapes are said to contain random-access memory (RAM) because the information on them can be searched or replaced with ease.

Some other types of file storage devices contain read-only memory (ROM)--information that the computer cannot change.  ROM units may consist of a compact disc, a cartridge, or a silicon chip.  They are used to store large databases and programs for computer games.

A popular method of storing large volumes of information is known as CD-ROM (Compact Disc Read-Only Memory).  CD-ROM's store information for computers much as audio compact discs store music.  The surface of the disc consists of small indentations and flat spaces that represent the 1's and 0's of binary code.  CD-ROM's require special players to read them.  A typical CD-ROM can store the equivalent of thousands of printed pages.  Information on CD-ROM may include text, pictures, sound, and even moving pictures.  Programs that combine several of these forms of information are called multimedia programs.

Programming a Computer

Programming involves the preparation and writing of detailed instructions for a computer.  These instructions tell the computer exactly what data to use and what sequence of operations to perform with the data.  Without programs, a computer could not solve problems or deliver any other desired result.

Some people prepare their own computer programs.  But in many cases, computer scientists and other computer specialists called programmers write instructions for computers.  They use programming languages that consist of letters, words, and symbols, as well as rules for combining those elements.

A computer cannot work directly with a program written in a programming language.  The instructions must be translated into a machine language composed of binary digits.  These digits represent operation codes, memory addresses, and various symbols, such as plus and minus signs.  Machine language is also known as low-level language.

Special programs called compilers and assemblers translate programming languages into machine language.  Another special type of program called an operating system contains instructions for the operation of a computer.  It controls the input and output devices, and it reads and responds to user commands.  It also places programs and data into the memory and makes sure that the processor executes the right programs.  Thus, the operating system combines the many separate parts of a computer into a single useful system.

Compilers, assemblers, and operating systems may be viewed as "smart programs" because they enable a computer to understand complicated instructions.  The user communicates with the smart program, and the smart program communicates with the computer.  A computer combined with a smart program acts like a different, smarter computer.  This combination is called a virtual machine.

Preparing a Program begins with a complete description of the job that the computer is to perform.  This job description is obtained from the person for whom the program is being prepared, such as a business manager or an engineer.  It explains what input data are needed, what computing must be done, and what the output should be.  Computer programmers use the description to prepare diagrams and other pictorial aids that represent the steps needed to complete the task.  The programmers may produce a diagram called a systems flow chart that shows how all the major parts of the job fit together systematically.

After a computer program is written, it is tested on the computer for mistakes.  Computer experts refer to mistakes in programs as "bugs" and the testing of programs as "debugging."

A program generally is entered into a computer in what is known as an interactive environment.  In such an environment, the programmer enters part of the program on a computer terminal.  The computer's operating system responds immediately, telling the programmer how the computer will interpret each instruction.  The programmer then can analyze each response.  Programs that result from this interaction between the programmer and the computer generally are stored on some type of file storage device until needed.

Using Programming Languages.  Computers appear to work directly with programming languages.  But the smart program, not the computer, actually understands these languages.  The smart program translates a program into machine language.  The program then enters the translated version into the computer's memory.  The processor reads and executes each translated instruction.

There are many different high-level programming languages.  Some of them closely resemble the language of mathematics.  Others enable programmers to use symbols and various everyday expressions, such as "READ," "PRINT," and "STOP." All high-level languages are designed to let the programmer concentrate on the basic ideas of a task rather than on the details.

The language that a programmer uses depends largely on the job to be done.  If a task involves processing business data, the programmer would most likely use COBOL (COmmon Business Oriented Language).  However, programming a computer to solve complicated scientific problems might require the use of a mathematically oriented language, such as FORTRAN (FOrmula TRANslation).

Some high-level languages can be used for business, technical, or scientific programming.  Such languages include APL (A Programming Language); C; and LISP (LISt Processor).

Another commonly used programming language is BASIC (Beginner's All-purpose Symbolic Instruction Code).  This programming language is well suited for writing relatively simple programs for personal computers.  Many elementary schools and high schools that offer a course in programming teach BASIC because it is easy to learn and to use.  Pascal, named for the French mathematician and scientist Blaise Pascal, also is taught in many schools.

Some computer programs may be written in an assembly language.  This kind of language is harder to use than a high-level language.  The programmer must state each instruction very precisely, with much more detail than is needed when using a high-level language.

The Computer Industry

The manufacture, development, sales, and servicing of computer hardware and software make up one of the largest and most important industries in the world.  Governments, institutions, and virtually all industries rely upon computers.  By the year 2000, the computer industry is expected to be the second largest industry in the world in terms of annual revenue.  Only agriculture will be larger.

The first commercial digital computers were manufactured in the 1950's.  Throughout the 1950's, as the importance of computers increased, people's acceptance of them increased as well.  More than 10,000 computers were in operation by 1961.  Ten years later, the number of computers exceeded 100,000.  By 1990, there were about 100 million data-processing computers--that is, computers that require input and output equipment--in operation worldwide.

The United States has the largest computer industry in the world, employing more than 1 million people.  It also has more computers than any other country--more than 50 million, or about half the world's computers.  Japan ranks second with more than 9 million computers, about 11 per cent of the world total.  European countries account for nearly 25 per cent of all computers.

The economic growth of the computer industry has matched the increase in the number of computers.  The United States produced about $1 billion worth of computers in 1958.  Ten years later, the figure had reached $4.8 billion.

In the late 1970's, the computer industry's rate of growth increased dramatically.  Advances in both computer technology and manufacturing technology enabled the United States to sell computers worth more than $30 billion in 1981.  By 1990, the U.S. computer industry's annual revenues had topped $100 billion, and they continued to grow.

Manufacturing.  From a few dozen companies in the early 1960's, the computer industry has grown to more than 10,000 firms around the world.  These companies manufacture computers and such peripheral equipment as modems and printers.  They also develop and publish software and provide various computer supplies, such as magnetic disks.

Some companies produce entire computer systems, ranging from personal computers to supercomputers.  Many companies manufacture computer components, including processors.  Some companies produce input and output equipment, such as terminals and printers.  Other important products of the computer industry include equipment that increases a computer's abilities to provide visual and audio output, and the network boards and cables used to create computer networks.

The largest computer manufacturer in the United States--and the world--is International Business Machines Corporation (IBM).  By the early 1990's, IBM's annual sales had reached nearly $65 billion.  The Hewlett-Packard Company ranks second in the United States, followed closely by Digital Equipment Corporation (DEC).  Both companies had more than $14 billion in annual sales in the early 1990's.  Other leading U.S. computer makers include Unisys, Apple Computer Incorporated, Compaq Computer Corporation, and Sun Microsystems Incorporated.

The largest computer manufacturer outside the United States is Japan's Fujitsu, followed closely by NEC Corporation, also of Japan.  Each company had sales of more than $9 billion in 1988.  The leading computer companies in Europe include Groupe Bull of France, Italy's Olivetti, and Siemens AG of Germany.

Research and Development.  The constant increase in computer power is a major reason for the computer industry's success.  Such increases result from computer science research and development, which take place at businesses and universities throughout the world.

One area of great interest to computer researchers and manufacturers is memory speed and capacity.  As software becomes more complex, it requires more computer memory in order to operate properly.  At the same time, sophisticated software can manipulate increasingly large amounts of data, which occupy more space in the computer's memory.

The storage of information files is another important area of study.  Researchers work to develop increasingly compact ways to store data, such as on magnetic disks, compact discs, or other devices.

Artificial intelligence is an exciting area of software research.  Experts in this field design computer systems to perform tasks that appear to require intelligence, such as reasoning and learning.  In this manner, artificial intelligence experts hope to increase the ability of computers to respond to problems in a "human" manner.

Sales.  Computers are sold in a variety of ways.  Large manufacturers of computers have teams of sales professionals.  These teams call on corporations and institutions, analyze their needs, and provide the appropriate combination of hardware and software.

Another method of selling computers involves a value-added reseller (VAR).  A VAR purchases computer systems and components from a variety of sources.  It then sells the finished products to computer users.

Retail outlets play an increasingly important role in the sale of personal computers.  Computer stores, mail-order houses, and general merchandise stores also sell many computers.

Service and Repair.  Because people depend on their computers, it is important to have the machines serviced periodically and repaired promptly when necessary.  Many computer manufacturers offer service contracts that provide for regular maintenance and prompt repairs.  When a large computer system breaks down, service technicians must visit the computer itself.  Some large businesses and institutions have their own computer maintenance staffs.

Careers.  There are many career opportunities in the computer industry.  Computer engineers are probably the most technically specialized computer experts.  Hardware engineers design the circuits that are engraved on chips, and they develop and design the wiring that lets information flow smoothly through the computer.  Engineers also design the technical aspects of memory, file storage, and peripheral equipment.

Computer programmers write the instructions that make computers operate properly.  Systems analysts determine the most efficient use of computers for a particular situation.  They study entire computer systems--hardware and software--and the purpose a computer is intended to serve.

Software publishers make up another career area.  People in this field issue programs, write and edit instruction manuals, and provide technical services for customers.

Many career opportunities in computers exist outside the computer industry itself.  For example, data processors enter information into computers.  Workers in many industries oversee the computers that control machines.

Some of the industry's most successful individuals are self-taught.  But most computer careers call for a college degree.  College courses that help prepare students for careers in computers include programming, electrical engineering, systems analysis, and data processing.

The Development of the Computer

The ideas and inventions of many engineers, mathematicians, and scientists led to the development of the computer.  The ancient abacus served as the earliest sort of calculating device.  But its use was limited by the need to move each counter individually.

Early Calculating Devices.  The first true calculating machines were developed in the 1600's.  In 1642, the French mathematician, scientist, and philosopher Blaise Pascal invented the first automatic calculator.  The device performed addition and subtraction by means of a set of wheels linked to each other by gears.  The first wheel represented the numbers 1 to 10, the second wheel represented 10's, the third stood for 100's, and so on.  When the first wheel was turned 10 notches, a gear moved the second wheel forward a single notch.  The other wheels became engaged in a similar manner.

During the early 1670's, the German mathematician Gottfried Wilhelm von Leibniz extended the usefulness of the calculator that Pascal had invented.  Leibniz's improvements included gear and wheel arrangements that made multiplication and division possible.

Leibniz also sought a counting system that would be easier for a machine to handle than the decimal system.  He developed the binary system of mathematics in the late 1600's.  Binary mathematics uses only the 0 and the 1, arranging them to represent all numbers.

An important contribution to the development of binary mathematics was made in the mid-1800's by George Boole, an English logician and mathematician.  Boole used the binary system to invent a new type of mathematics.  Boolean algebra and Boolean logic perform complex mathematical and logical operations on the symbols 0 and 1.  Thus, a mechanical representation of binary mathematics would require the representation of only those two digits.  This advance shaped the development of computer logic and computer languages.

Early Punched-Card Computing Devices.  A French textile weaver named Joseph Marie Jacquard made the next great contribution to the development of the computer.  In the weaving process, needles directed thread to produce patterns.  In 1801, Jacquard invented the Jacquard loom, which used punched cards to automate this process for the first time.  The cards had patterns of holes punched in them, and were placed between the rising needles and the thread.  The presence or absence of a hole could be compared to the two digits of the binary system.  Where there were holes, the needles rose and met the thread.  Where there were no holes, the needles were blocked.  By changing cards and alternating the patterns of punched holes, it became possible to mechanically create complex woven patterns.

The punched cards of the Jacquard loom inspired the English mathematician Charles Babbage.  During the 1830's, Babbage developed the idea of a mechanical computer that he called an analytical engine.  He worked on the machine for almost 40 years.  When performing complex computations or a series of calculations, the analytical engine would store completed sets of punched cards for use in later operations.  Babbage's analytical engine contained all of the basic elements of an automatic computer--storage, working memory, a system for moving between the two, and an input device.  But the technology of Babbage's time was not advanced enough to provide the precision parts he needed to construct the machine, and he lacked funding for the project.  Babbage, like others of his time, also lacked an understanding of the nature and use of electricity.

The First Successful Computer.  In 1888, American inventor and businessman Herman Hollerith devised a punched card system, including the punching equipment, for tabulating the results of the United States census.  Hollerith's machines used electrically charged nails that, when passed through a hole punched in a card, created a circuit.  The circuits registered on another part of the machine, where they were read and recorded.  Hollerith's machines tabulated the results of the 1890 census, making it the fastest and most economical census to date.  In a single day, 56 of these machines could tabulate census information about more than 6 million people.

Hollerith's tabulator achieved widespread success.  Governments, institutions, and industries found uses for the machine.  In 1896, Hollerith founded the Tabulating Machine Company.  He continued to improve his machines during the following years.  In 1911, he sold his share of the company.  Its name was changed to the Computing-Tabulating-Recording Company (C-T-R).  In 1924, the name was changed to International Business Machines Corporation (IBM).

The First Analog Computer.  Vannevar Bush, an American electrical engineer, worked to develop a computer that would help scientists.  In 1930, he built a device called a differential analyzer to solve differential equations.  This machine was the first reliable analog computer.  It derived measurements from the movements of its gears and shafts.

The First Electronic Computers.  Some scientists and engineers saw greater computing potential in electronics.  The first special-purpose electronic digital computer was constructed in 1939 by John V. Atanasoff, an American mathematician and physicist.  In 1944, Howard Aiken, a Harvard University professor, built another early form of digital computer, which he called the Mark I. The operations of this machine were controlled chiefly by electromechanical relays (switching devices).

In 1946, two engineers at the University of Pennsylvania, J. Presper Eckert, Jr., and John William Mauchly, built the first general-purpose electronic digital computer.  They called it ENIAC (Electronic Numerical Integrator And Computer).  ENIAC contained about 18,000 vacuum tubes, which replaced the relays that had controlled the operation of Mark I. The machine weighed more than 30 tons (27 metric tons), occupied more than 1,500 square feet (140 square meters) of floor space, and consumed 150 kilowatts of electricity during operation.  ENIAC operated about 1,000 times as fast as the Mark I. It could perform about 5,000 additions and 1,000 multiplications per second.  ENIAC also could store parts of its programming.

Although ENIAC performed its work rapidly, programming the huge machine took a great deal of time.  Eckert and Mauchly next worked on developing a computer that could store even more of its programming.  They worked with John von Neumann, a Hungarian-born American mathematician.  Von Neumann helped assemble all available knowledge of how the logic of computers should operate.  He also helped outline how stored programming would improve performance.  In 1951, a computer based on the work of the three men became operational.  It was called EDVAC (Electronic Discrete Variable Automatic Computer).  EDVAC strongly influenced the design of later computers.

Also in 1951, Eckert and Mauchly invented a more advanced computer called UNIVAC I (UNIVersal Automatic Computer).  Within a few years, UNIVAC I became the first commercially available computer.  Unlike earlier computers, UNIVAC I handled both numbers and alphabetical characters equally well.  It also was the first computer system in which the operations of the input and output equipment were separated from those of the computing unit.  UNIVAC I used vacuum tubes to perform arithmetic and memory-switching functions.

The first UNIVAC I was installed at the U.S. Bureau of the Census in June 1951.  The following year, another UNIVAC I was used to tabulate the results of the United States presidential election.  Based on available data, UNIVAC I accurately predicted the election of President Dwight D. Eisenhower less than 45 minutes after the polls closed.

The Miniaturization of Computer Components.  The invention of the transistor in 1947 led to the production of faster and more reliable electronic computers.  Transistors control the flow of electric current in electronic equipment.  They soon replaced the bulkier, less reliable vacuum tubes.  In 1958, Control Data Corporation introduced the first fully transistorized computer, designed by American engineer Seymour Cray.  IBM introduced its first transistorized computers in 1959.

Miniaturization continued with the development of the integrated circuit in the early 1960's.  An integrated circuit contains thousands of transistors and other tiny parts on a small chip.  This device enabled engineers to design both minicomputers and high-speed mainframes with tremendous memory capacities.

Despite the shrinking size of their components, most computers remained relatively large and expensive.  But dependence on computers increased dramatically.  By the late 1960's, many large businesses relied on computers.  Many companies linked their computers together into networks, making it possible for different offices to share information.

During the 1960's, computer technology improved rapidly.  Different kinds of circuits were placed on silicon chips.  Some of the circuits contained the computer's logic.  Other chips held memory.  By the early 1970's, the entire workings of a computer could be placed on a handful of chips.  As a result, smaller computers became possible.  The central chip that controlled the computer became known as a microprocessor.

The Personal Computer.  The first personal computer, the Altair, was introduced in 1975.  Only electronics hobbyists bought these computers.

In 1977, two American students, Steven P. Jobs and Stephen G. Wozniak, founded the Apple Computer Company and introduced the Apple II personal computer.  The Apple II was much less expensive than mainframes.  As a result, computers became available to people other than computer specialists and technicians.  Personal computers were purchased by small and medium-sized businesses that could not afford mainframes or did not need the immense computing power that mainframes provided.  Millions of individuals, families, and schools also bought them.

In 1981, IBM entered the personal computer market with its PC. The machine was even more successful than the Apple II. Apple scored another success in 1984 with the introduction of its Macintosh, a powerful, easy-to-use desktop computer.

As computer power increased, so did computer speed.  These increases were accompanied by a steady reduction in both size and cost.  Modern personal computers are more powerful than UNIVAC I and can be purchased for less than $1,000.

Computers of the Future.  Tomorrow's computers will be increasingly powerful.  Computer researchers continue to seek ways to develop faster and more powerful machines and software.  For example, experimental computers called optical processors use beams of laser light, rather than electric current, to process data.  Many scientists believe that optical computers will someday work much faster than electronic ones.  Much software research focuses on the development of new virtual-reality programs to provide increasingly realistic simulated experiences.  Computer experts predict that virtual reality will play a large role in education and training as well as offer dramatic possibilities for entertainment.  Much software research also focuses on the further development of artificial intelligence, which is intended to help computers make decisions rather than simply to manipulate data.  One type of artificial intelligence, the expert system, translates patterns of experience into software.  An expert system responds to input by asking questions and providing responses.  In this manner, it constantly narrows the field of inquiry until a solution is achieved.

Much effort also is being devoted to making computers smaller.  In the near future, most experts feel that computers will continue to be built from integrated circuits.  But some scientists foresee the production of biological computers, which will be grown rather than manufactured.  In addition, some experts believe that computer technology will develop methods of storing data on individual molecules.  A molecular storage system could contain all of the knowledge of the human race in a space smaller than a paperback book.

Problems of the Computer Age

Because computers provide such convenient storage for large amounts of information, less and less information is stored on paper.  Much of the convenience of computers stems from their ability to form networks by means of telephone lines.  But a computer that makes up part of a network resembles a room with many doors.  Intruders who slip through these "doors" are difficult to trace.  For this reason, computer designers work to safeguard stored information from unauthorized access, as well as from system breakdown or failure.

Computers and Privacy.  Many people fear that their right to privacy is threatened by the possible misuse or unauthorized disclosure of information in computer databases.  Databases often contain private and personal information, such as medical, banking, or tax records.  Other databases pertain to business plans or inventions that a company must conceal from competing companies.  Still other databases store top-secret military information or other kinds of data important to a nation's security.  Today, laws control the disclosure of data.

Computers and Security.  Computer operating systems are designed to prevent unauthorized entry into a computer, but computer crimes sometimes occur.  Industrial spies and thieves often use telephone lines to gain access to computers.  Some of these criminals steal or change the information in a computer database.  Others steal money by using the capability of computers to transfer funds electronically from one account to another.  Major problems can result if someone obtains illegal access to secret information in government or corporate databases.  Sometimes, people within an organization commit computer crimes.  Other crimes are committed by outsiders who create chaos by breaking into computer systems.

In the late 1980's, computer experts became aware of a dangerous type of program called a computer virus.  A computer virus is designed to do mischief, sometimes by deleting or changing information and sometimes by simply inserting a message.  A virus eventually enters a computer's operating system.  It spreads by rapidly making copies of itself, thus "infecting" the other computer systems in a network.  This process can quickly overload huge computer networks.

Various methods help safeguard computer systems and databases.  Protective measures are built into many computer operating systems to prevent access by invaders.  Many computers require a user to enter a secret password.  Some systems automatically scramble information so that it can only be decoded by authorized personnel.  Careful protection of these passwords and codes helps decrease the likelihood of illegal access.  Antivirus programs are available to prevent computer viruses from doing mischief.

Other Problems.  Computers are valuable in many ways.  But if a computer breaks or is damaged, the people who rely on it face great difficulties.  Until the computer is fixed, these people may be worse off than if they never had a computer at all.  For example, information may be lost if a computer system suffers damage in a natural disaster, such as a fire or flood.  Computer breakdowns and faulty programming in business organizations delay transactions, disrupt work, and create inconveniences for consumers.  An undetected computer malfunction that occurs at an air traffic control center could cause a collision.  A computer failure at a national defense installation could have even more serious consequences.

Computers, together with their programs, are the most complicated machines in history--and, arguably, the most useful.  As computers become more powerful and widespread, computer education must continue to increase as well.

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