Generally, a computer is any device that can perform numerical calculations even an adding machine, an abacus, or a slide rule. Currently, however, the term usually refers to an electronic device that can use a list of instructions, called a program, to perform calculations or to store, manipulate, and retrieve information.

Today's computers are marvels of miniaturization. Machines that once weighed 30 tons and occupied warehouse-size rooms now may weigh as little as three pounds (1.4 kilograms) and can be carried in a suit pocket. The heart of today's computers are integrated circuits (ICs), sometimes called microchips, or simply chips. These tiny silicon wafers can contain millions of microscopic electronic components and are designed for many specific operations: some control an entire computer (CPU, or central processing unit, chips); some perform millions of mathematical operations per second (math coprocessors); others can store more than 16 million characters of information at one time (memory chips).

In 1953 there were only about 100 computers in use in the entire world. Today hundreds of millions of computers form the core of electronic products, and more than 110 million programmable computers are being used in homes, businesses, government offices, and universities for almost every conceivable purpose.

Computers come in many sizes and shapes. Special-purpose, or dedicated, computers are designed to perform specific tasks. Their operations are limited to the programs built into their microchips. These computers are the basis for electronic calculators and can be found in thousands of other electronic products, including digital watches (controlling timing, alarms, and displays), cameras (monitoring shutter speeds and aperture settings), and automobiles (controlling fuel injection, heating, and air conditioning and monitoring hundreds of electronic sensors).

General-purpose computers, such as personal computers and business computers, are much more versatile because they can accept new sets of instructions. Each new set of instructions, or program, enables the same computer to perform a different type of operation. For example, one program lets the computer act like a word processor, another lets it manage inventories, and yet another transforms it into a video game.

Although some general-purpose computers are as small as pocket radios, the smallest class of fully functional, self-contained computers is the class called notebook computers. These usually consist of a CPU, data-storage devices called disk drives, a liquid-crystal display (LCD), and a full-size keyboard all housed in a single unit small enough to fit into a briefcase.

Today's desktop personal computers, or PCs, are many times more powerful than the huge, million-dollar business computers of the 1960s and 1970s. Most PCs can perform from 16 to 66 million operations per second, and some can even perform more than 100 million. These computers are used not only for household management and personal entertainment, but also for most of the automated tasks required by small businesses, including word processing, generating mailing lists, tracking inventory, and calculating accounting information.

Minicomputers are fast computers that have greater data manipulating capabilities than personal computers and can be used simultaneously by many people. These machines are primarily used by larger businesses to handle extensive accounting, billing, and inventory records.

Mainframes are large, extremely fast, multi-user computers that often contain complex arrays of processors, each designed to perform a specific function. Because they can handle huge databases, can simultaneously accommodate scores of users, and can perform complex mathematical operations, they are the mainstay of industry, research, and university computing centres.

The speed and power of supercomputers, the fastest class of computer, are almost beyond human comprehension, and their capabilities are continually being improved. The most sophisticated of these machines can perform nearly 32 billion calculations per second, can store a billion characters in memory at one time, and can do in one hour what a desktop computer would take 40 years to do. Supercomputers attain these speeds through the use of several advanced engineering techniques. For example, critical circuitry is super cooled to nearly absolute zero so that electrons can move at the speed of light, and many processors are linked in such a way that they can all work on a single problem simultaneously. Because these computers can cost millions of dollars, they are used primarily by government agencies and large research centres.

Computer development is rapidly progressing at both the high and the low ends of the computing spectrum. On the high end, by linking together networks of several small computers and programming them to use a language called Linda, scientists have been able to outperform the supercomputer. This technology is called parallel processing and helps avoid hours of idle computer time. A goal of this technology is the creation of a machine that could perform a trillion calculations per second, a measure known as a teraflop. On the other end of the spectrum, companies like Apple and Compaq are developing small, handheld personal digital assistants (PDAs). The Apple Newton, for example, lets people use a pen to input handwritten information through a touch-sensitive screen and to send mail and faxes to other computers. Researchers are currently developing microchips called digital signal processors, or DSPs, to enable these PDAs to recognize and interpret human speech. This development, which will permit people in all professions to use a computer quickly and easily, promises to lead to a revolution in the way humans communicate and transfer information.

Computers at Work Applications

Communication. Computers make all modern communication possible. They operate telephone switching systems, coordinate satellite launches and operations, help generate special effects for movies, and control the equipment in all phases of television and radio broadcasts. Local-area networks (LANs) link the computers in separate departments of businesses or universities, and larger networks, such as the Internet, permit modems telecommunication devices that transmit data through telephone lines to link individual computers to other computers anywhere in the world. Journalists and writers now use word processors to write books and articles, which they then submit to publishers on magnetic disks or through telephone lines. The data may then be sent directly to computer-controlled typesetters, some of which actually design the layout of printed pages on computer screens.

Science and research. Computers are used by scientists and researchers in many ways to collect, store, manipulate, and analyze data. Running simulations is one of the most important applications. Data representing a real-life system is entered into the computer, and the computer manipulates the data in order to show how the natural system is likely to behave under a variety of conditions. In this way scientists can test new theories and designs or can examine a problem that does not lend itself to direct experimentation. Computer-aided design, or CAD, programs enable engineers and architects to design three-dimensional models on a computer screen. Chemists may use computer simulation to design and test molecular models of new drugs. Some simulation programs can generate models of weather conditions to help meteorologists make predictions. Flight simulators are valuable training tools for pilots.

Industry. Computers have opened a new era in manufacturing and consumer-product development. In the factory, computer-assisted manufacturing, or CAM, programs help people plan complex production schedules, keep track of inventories and accounts, run automated assembly lines, and control robots. Dedicated computers are routinely used in thousands of products ranging from calculators to airplanes.

Government. Government agencies are the largest users of mainframes and supercomputers. The United States Department of Defence uses computers for hundreds of tasks, including research, breaking codes, interpreting data from spy satellites, and targeting missiles. The Internal Revenue Service uses computers to keep track of tens of millions of tax returns. Computers are also essential for taking the census, maintaining criminal records, and other tasks.

Education. Computers have proved to be valuable educational tools. Computer-assisted instruction, or CAI, uses computerized lessons that range from simple drills and practice sessions to complex interactive tutorials. These programs have become essential teaching tools in medical schools and military training centres, where the topics are complex and the cost of human teachers is extremely high. Educational aids, such as some encyclopaedias and other major reference works, are available to personal-computer users either on magnetic disks or optical discs or through various telecommunication networks.

Arts and Entertainment. Video games are one of the most popular applications of personal computers. The constantly improving graphics and sound capabilities of personal computers have made them popular tools for artists and musicians. Personal computers can display millions of colours, can produce images far clearer than those of a television set, and can connect to various musical instruments and synthesizers. Painting and drawing programs enable artists to create realistic images and animated displays much more easily than they could with more traditional tools. "Morphing" programs allow photographers and filmmakers to transform photographic images into any size and shape they can imagine. High-speed supercomputers can insert life-like animated images into frames of a film so seamlessly that movie-goers cannot distinguish real actors from computer-generated images. Musicians can use computers to create multiple-voice compositions and to play back music with hundreds of variations. Speech processors even give a computer the ability to talk and sing.

Types of Computers

There are two fundamentally different types of computers analogue and digital. (Hybrid computers combine elements of both types.) Analogue computers solve problems by using continuously changing data (such as pressure or voltage) rather than by manipulating discrete binary digits (1s and 0s) as a digital computer does. In current usage, the term computer usually refers to digital computers. Digital computers are generally more effective than analogue computers for four principal reasons: they are faster; they are not as susceptible to signal interference; they can convey data with more precision; and their coded binary data are easier to store and transfer than are analogue signals.

Analogue computers. Analogue computers work by translating constantly changing physical conditions (such as temperature, pressure, or voltage) into corresponding mechanical or electrical quantities. They offer continuous solutions to the problems on which they are operating. For example, an automobile speedometer is a mechanical analogue computer that measures the rotations per minute of the drive shaft and translates that measurement into a display of miles per hour. Electronic analogue computers in chemical plants monitor temperatures, pressures, and flow rates and send corresponding voltages to various control devices, which, in turn, adjust the chemical processing conditions to their proper levels.

Digital computers. For all their apparent complexity, digital computers are basically simple machines. Every operation they perform, from navigating a spacecraft to playing a game of chess, is based on one key operation determining whether certain switches, called gates, are open or closed. The real power of a computer lies in the speed with which it checks these switches anywhere from 1 million to 4 billion times, or cycles, per second.

A computer can recognize only two states in each of its millions of circuit switches on or off, or high voltage or low voltage. By assigning binary numbers to these states 1 for on and 0 for off, for example and linking many switches together, a computer can represent any type of data from numbers to letters to musical notes. This process is called digitization.

Imagine that a computer is checking only one switch at a time. If the switch is on, it symbolizes one operation, letter, or number; if the switch is off it represents another. When switches are linked together as a unit, the computer can recognize more data in each cycle. For example, if a computer checks two switches at once it can recognize any of four pieces of data one represented by the combination off-off; one by off-on; one by on-off; and one by on-on. The more switches a computer checks in each cycle, the more data it can recognize at one time and the faster it can operate. Below are some common groupings of switches (each switch is called a binary digit, or bit) and the number of discrete units of data that they can symbolize:

4 bits = a nibble (16 pieces of data);

8 bits = a byte (256 pieces of data);

16 bits = a word (65,536 pieces of data).

32 bits = a double word (4,294,967,296 pieces of data).

A byte is the basic unit of data storage because all characters, numbers, and symbols on a keyboard can be symbolized by using a combination of only eight 0s and 1s.

Each combination of ons and offs represents a different instruction, part of an instruction, or type of data (number, letter, or symbol). For example, depending on its context in a program, a byte with a pattern of 01000001 may symbolize the number 65, the capital letter A, or an instruction to the computer to move data from one place to another.

PARTS OF A DIGITAL COMPUTER SYSTEM

A digital computer is a complex system of four functionally different elements a central processing unit, input devices, memory-storage devices, and output devices linked by a communication network, or bus. These physical parts and all their physical components are called hardware.

Without a program, a computer is nothing but potential. Programs, also called software, are detailed sequences of instructions that direct the computer hardware to perform useful operations.

Hardware

The central processing unit, or CPU, is the heart of a computer. In addition to performing arithmetic and logic operations on data, it times and controls the rest of the system. Mainframe CPUs sometimes consist of several linked microchips, each performing a separate task, but most other computers require only a single microprocessor as a CPU.

Most CPU chips and microprocessors have four functional sections:

(1) the arithmetic/logic unit, which performs arithmetic operations (such as addition and subtraction) and logic operations (such as testing a value to see if it is true or false);

(2) temporary storage locations, called registers, which hold data, instructions, or the results of calculations;

(3) the control section, which times and regulates all elements of the computer system and also translates patterns in the registers into computer activities (such as instructions to add, move, or compare data); and

(4) the internal bus, a network of communication lines that links internal CPU elements and offers several different data paths for input from and output to other elements of the computer system.

Input devices let users enter commands, data, or programs for processing by the CPU. Computer keyboards, which are much like typewriter keyboards, are the most common input devices. Information typed at the keyboard is translated into a series of binary numbers that the CPU can manipulate. Another common input device, the mouse, is a mechanical or opto-mechanical device with buttons on the top and a rolling ball in its base. To move the cursor on the display screen, the user moves the mouse around on a flat surface. The user selects operations, activates commands, or creates or changes images on the screen by pressing buttons on the mouse. Other input devices include joysticks and trackballs. Light pens can be used to draw or to point to items or areas on the display screen. A sensitized digitizer pad translates images drawn on it with an electronic stylus or pen into a corresponding image on the display screen. Touch-sensitive display screens allow users to point to items or areas on the screen and to activate commands. Optical scanners "read" characters on a printed page and translate them into binary numbers that the CPU can use. Voice-recognition circuitry digitizes spoken words and enters them into the computer.

Memory-storage devices. Most digital computers store data both internally, in what is called main memory, and externally, on auxiliary storage units. As a computer processes data and instructions, it temporarily stores information internally, usually on silicon random-access memory, or RAM, chips often called semiconductor memory. Usually mounted on the main circuit board inside the computer or on peripheral cards that plug into the board, each RAM chip may consist of as many as 16 million switches, called flip-flop switches, that respond to changes in electric current. Each switch can hold one bit of data: high voltage applied to a switch causes it to hold a 1; low voltage causes it to hold a 0. This kind of internal memory is also called read/write memory.

Another type of internal memory consists of a series of read-only memory, or ROM, chips. The switches of ROM chips are set when they are manufactured and are unchangeable. The patterns on these chips correspond to commands and programs that the computer needs in order to boot up, or ready itself for operation, and to carry out basic operations. Because read-only memory is actually a combination of hardware (microchips) and software (programs), it is often referred to as firmware.

Other devices that are sometimes used for main memory are magnetic-core memory and magnetic-bubble memory. Unlike semiconductor memories, these do not lose their contents if the power supply is cut off. Long used in mainframe computers, magnetic-core memories are being supplanted by the faster and more compact semiconductor memories in mainframes designed for high-speed applications. Magnetic-bubble memory is used more often for auxiliary storage than for main memory.

Auxiliary storage units supplement the main memory by holding parts of programs that are too large to fit into the random-access memory at one time. They also offer a more permanent and secure method for storing programs and data.

Four auxiliary storage devices floppy disks, hard disks, magnetic tape, and magnetic drums store data by magnetically rearranging metal particles on disks, tape, or drums. Particles oriented in one direction represent 1s, and particles oriented in another direction represent 0s. Floppy-disk drives (which "write" data on removable magnetic disks) can store from 140,000 to 2.8 million bytes of data on one disk and are used primarily in laptop and personal computers. Hard disk drives contain non removable magnetic media and are used with all types of computers. They access data very quickly and can store from 10 million bytes (10 megabytes) of data to a few gigabytes (billion bytes).

Magnetic-tape storage devices are usually used together with hard disk drives on large computer systems that handle high volumes of constantly changing data. The tape drives, which access data very slowly, regularly back up, or duplicate, the data in the hard disk drives to protect the system against loss of data during power failures or computer malfunctions.

Magnetic-drum memories store data in the form of magnetized spots in adjacent circular tracks on the surface of a rotating metal cylinder. They are relatively slow and are rarely used today.

Optical discs are nonmagnetic auxiliary storage devices that developed from compact-audio-disc technology. Data is encoded on a disc as a series of pits and flat spaces, called lands, the lengths of which correspond to different patterns of 0s and 1s. One removable 4 3/4-inch (12-centimetre) disc contains a spiral track more than 3 miles (4.8 kilometres) long, on which can be stored nearly a billion bytes (gigabyte) of information. All of the text of an encyclopaedia, for example, would fill only one fifth of one disc. Read-only optical discs, whose data can be read but not changed, are called CD-ROMs (compact disc-read-only memory). Recordable CD-ROM drives, called WORM (write-once/read-many) drives, are used by many businesses and universities to periodically back up changing databases and to conveniently distribute massive amounts of information to customers or users.

Circa 1995

Continuing … 'COMPUTER (Part 2 of 3)'

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