Английский язык. Основы компьютерной грамотности 142

A MODEM

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The piece of equipment that allows a computer to commu­nicate with other computers over telephone lines is called a modem. The modem allows the individual to access informa­tion from all over the world and use that information in every­day life. Connecting with banks, Automatic Teller Machines, cash registers to read credit cards, access travel agents, buy prod­ucts, e-mail, access databases, and teleconferencing, the mo­dems provide easy access to many services. Files can be trans­ferred easily, by uploading to another machine, or downloading to your own machine within a matter of minutes. The comput­er modem can be used as a telephone answering system, and documents can be faxed from one computer to another assur­ing fast and easy access to important documents.

A modem takes computer information and changes it into a signal that can be sent over telephone lines. The modem is a bridge between digital and analog signals. The computer is of

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the digital type, and the telephone using analog technology. The modem converts the "0"s and "l"s of the computer (off-on switches) into an analog signals modulating the frequency of the electronic wave or signal. The modem does just the opposite and demodulate the signal back into digital code. The modem gets its name from MOdulate and the DEModulate.

Most people believe that you need a separate phone line for a modem, but that is not true.Your modem and telephone can share one line, the problem arises when someone else needs to use the tele­phone while the modem is in use. Also disable call waiting, it could disrupt your modem connection while the modem is in use.

There are three kinds of modems — internal, external, and fax. All modems do the same thing, they allow computers to communicate through telephone lines. This lets computers ex­change information everywhere. Internal Modem is a circuit board that plugs into one of the expansion slots of the comput­er. Internal modems usually are cheaper than external modems, but when problems occur, fixing and troubleshooting the mo­dem can sometimes prove to be quite difficult. External Modem attaches to the back of the computer by way of a cable that plugs into the modem port. It is usually less expensive and very por­table. It can be used with other computers very easily by unplug­ging it and plugging it into another computer. Fax Modem can be hooked up to your telephone and used to send information to your computer. Your computer can also send information to a fax machine. Most computer modems are modems with fax­ing capabilities.

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MICROCOMPUTER SYSTEM ORGANIZATION

1. The organization of a microcomputer system is the same as that of a larger computer system. The microprocessor unit (MPU), usually concentrated in a single chip, consists of the control unit and the arithmetic logical unit. Internal memory

is made up of random access memory (RAM) and read-only memory (ROM). Because RAM is only temporary storage, all microcomputers require some instructions to get started after they are turned on, and these are contained in ROM. A micro­computer includes both an MPU and internal memory.

The portion of the system software that is in ROM brings into RAM the additional instructions required to operate the micro­computer. Typically these instructions are stored on a magnetic disk; hence, they are called a disk operating system, or DOS. This start-up process is called bootstrapping*. ROM also con­tains other programs that help to make personal computers easy to use, such as a programming language. Computer games are also stored in ROM cartridges.

In addition to the MPU, RAM, ROM, and associated con­trol circuits, other components, called peripheral devices, are needed to make a complete microcomputer system. The prin­cipal peripheral units are: input devices, output devices, mass storage units, and communication components. Like a DOS, the programs that control the flow of data between a microcom­puter and its peripheral devices are a part of systems software.

The most common input device used with personal comput­ers is the keyboard. Most personal computer keyboards have extra keys that perform special functions and that can be used to control the movement of a cursor on a screen. A leverlike** device, called a joystick, is also used as an input device, com­monly for playing video games.

2. The CRT (cathode-ray tube) screen used with personal computers is called a monitor. Keyboards and monitors may be part of a single unit that also contains the microcomputer and the disc drives, or they may be separate units. Besides the mon­itor, the most common input units are dot-matrix and letter-quality printers. Dot-matrix printers are suitable for most mi­crocomputer applications. Letter-quality printers are usually used for high-quality office correspondence. Both types of print­ers are considered to be low-speed character printers.

Mass storage units are available over a range of capacities and access times. Floppy disks, or diskettes, are the most common mass storage media. They store patterns of bits on magnetically coated, flexible plastic platters. A floppy disk platter is sealed permanently in a paper jacket with a small window for reading

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and writing. Hard disk storage systems are also available. They may be fixed or removable. Some mass storage units contain both floppy and hard disk devices.

Low-cost modulator-demodulator devices, called modems, that allow microcomputer systems to communicate over tele­phone lines have become increasingly popular. Modems permit networks of personal computer owners to exchange information or to access large data banks. These data banks may be dedi­cated to special applications, such as law or medicine, or they may provide a variety of consumer services.

Notes __________________________________________

* bootstrapping — начальная загрузка; ** leverlike — рычажковый

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