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

Ш________________________ Unit 10. Personal Computers

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.


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

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