.. 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 optomechanical 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 nonremovable 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 43/4-inch (12-centimeter) disc contains a spiral track more than 3 miles (4.8 kilometers) long, on which can be stored nearly a billion bytes (gigabyte) of information. All of the text in this encyclopedia, 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. Video display terminal Output devices let the user see the results of the computer’s data processing. The most common output device is the video display terminal (VDT), or monitor, which uses a cathode-ray tube (CRT) to display characters and graphics on a television-like screen. Modems (modulator-demodulators) are input-output devices that allow computers to transfer data between each other. A modem on one computer translates digital pulses into analog signals (sound) and then transmits the signals through a telephone line or a communication network to another computer.
A modem on the computer at the other end of the line reverses the process. Printers generate hard copy–a printed version of information stored in one of the computer’s memory systems. The three principal types of printers are daisy-wheel, dot-matrix, and laser. Other types of printers include ink-jet printers and thermal printers. Software A computer’s operating system is the software that allows all of the dissimilar hardware and software systems to work together. It is often stored in a computer’s ROM memory.
An operating system consists of programs and routines that coordinate operations and processes, translate the data from different input and output devices, regulate data storage in memory, allocate tasks to different processors, and provide functions that help programmers write software. Computers that use disk memory-storage systems are said to have disk operating systems (DOS). MS-DOS is the most popular microcomputer operating system. UNIX, a powerful operating system for larger computers, allows many users and many different programs to gain access to a computer’s processor at the same time. Visual operating systems called GUIs (graphical user interfaces) were designed to be easy to use, yet to give UNIX-like power and flexibility to home and small-business users. Future operating systems will enable users to control all aspects of the computer’s hardware and software simply by moving and manipulating their corresponding objects, or graphical icons displayed on the screen.
Sometimes programs other than the operating system are built into the hardware, as is the case in dedicated computers or ROM chips. Most often, however, programs exist independently of the computer. When such software is loaded into a general-purpose computer, it automatically programs the computer to perform a specific task–such as word processing, managing accounts and inventories, or displaying an arcade game. PCs and other Revolutions By the mid-1970s, microchips and microprocessors had drastically reduced the cost of the thousands of electronic components required in a computer. The first affordable desktop computer designed specifically for personal use was called the Altair 8800 and was sold by Micro Telemetry Systems in 1974.
In 1977 Tandy Corporation became the first major electronics firm to produce a personal computer. They added a keyboard and CRT to their computer and offered a means of storing programs on a cassette recorder. Soon afterward, a small company named Apple Computer, founded by engineer Stephen Wozniak and entrepreneur Steven Jobs, began producing a superior computer. IBM introduced its Personal Computer, or PC, in 1981. As a result of competition from the makers of clones (computers that worked exactly like an IBM-PC), the price of personal computers fell drastically. Today’s personal computer is 400 times faster than ENIAC, 3,000 times lighter, and several million dollars cheaper.
In rapid succession computers have shrunk from tabletop to lap-top and finally to palm size. With some personal computers, called pen-pads, people can even write directly on an etched-glass, liquid-crystal screen using a small electronic stylus , and words will appear on the screen in clean typescript. Multimedia In the early 1990s, manufacturers began producing inexpensive CD-ROM drives that could access more than 650 megabytes of data form a single disc. This development started a multimedia revolution that may continue for decades. The term multimedia encompasses the computer’s ability to merge sounds, video, text, music, animations, charts, maps, etc., into colorful, interactive presentations, a business advertising campaign, or even a space-war arcade game. Faster computers and the rapid proliferation of multimedia programs will probably forever change the way people get information.
The computer’s ability to instantly retrieve a tiny piece of information from the midst of a huge mass of data has always been one of its most important uses. Since video and audio clips can be stored alongside text on a single CD-ROM disc, a whole new way of exploring a subject is possible . By using hyperlinks–a programming method by which related terms, articles, pictures, and sounds are internally hooked together–material can be presented to people so that they can peruse it in a typically human manner, by association. For example, if you are reading about Abraham Lincoln’s Gettysburg Address and you want to read about the battle of Gettysburg, you need only click on the highlighted hyperlink battle of Gettysburg. Instantly, the appropriate text, photos, and maps appear on the monitor. Pennsylvania is another click away, and so on. Encyclopedias, almanacs, collections of reference books, interactive games using movie footage, educational programs, and even motion pictures with accompanying screenplay, actor biographies, director’s notes, and reviews make multimedia one of the computer world’s most exciting and creative fields.
The Information Superhighway A computer network is the interconnection of many individual computers, much as a road is the link between the homes and the buildings of a city. Having many separate computers linked on a network provides many advantages to organizations such as businesses and universities. People may quickly and easily share files; modify databases; send memos called E-mail, or electronic mail; run programs on remote mainframes; and get access to information in databases that are too massive to fit on a small computer’s hard drive. Networks provide an essential tool for the routing, managing, and storing of huge amounts of rapidly changing data. The Internet is a network of networks: the international linking of tens of thousands of businesses, universities, and research organizations with millions of individual users.
It is what United States President Al Gore first publicly referred to as the information superhighway. What is now known as the Internet was originally formed in 1970 as a military network called ARPAnet (Advanced Research Projects Agency network) as part of the Department of Defense. The network opened to non-military users in the 1970s, when universities and companies doing defense-related research were given access, and flourished in the late 1980s as most universities and many businesses around the world online. In 1993, when commercial providers were first permitted to sell Internet connections to individuals, usage of the network exploded. Millions of new users came on within months, and a new era of computer communications began. Most networks on the Internet make certain files available to other.
These common files can be databases, programs, or E-mail from the individuals on the network. With hundreds of thousands of international sites each providing thousands of pieces of data, it’s easy to imagine the mass of raw data available to users. The Internet is by no means the only way in which computer users can communicate with others. Several commercial online services provide connections to members who pay a monthly connect-time fee. CompuServe, America OnLine, Prodigy, Genie, and several others provide a tremendous range of information and services, including online conferencing, electronic mail transfer, program downloading, current weather and stock market information, travel and entertainment information, access to encyclopedias and other reference works, and electronic forums for specific users’ groups such as PC us Computers and Internet.