The modem

Chapter The modem

Teach Yourself Electricity and Electronics Third Edition Book
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Teach Yourself Electricity and Electronics Third Edition Book

  • The laser blinks rapidly while it scans a cylindrical drum. The drum has specialproperties that cause it to attract the printing chemical, called toner, in some places butnot others, creating an image pattern that will ultimately appear on the paper. A sheetof paper is pulled past the drum and also past an electrostatic charger. Toner from thedrum is attracted to the paper. The image thus goes onto the paper, although it has notyet been permanently fused, or bonded, to the paper. The fuser, a hot pair ofroller/squeezers, does this job, completing the printing process.The main asset of laser printers is their excellent print and graphics quality. The im-age resolution of a laser printer ranges from about 300 dots per inch (DPI) for older unitsto 1200, 2400, or even more DPI in state-of-the-art machines. As far as the untrained eyecan tell, 600 DPI is as good as a photograph. Laser printers can handle graphics and textequally well. If an image can be rendered on a photocopy machine, it can be renderedjust as well on a laser printer. Another asset of laser printers is that they make almost nonoise. Yet another good feature is that this type of printer is relatively fast. The best high-end machines can produce a couple of dozen copies per minute.The laser printer is the best device for rendering high-resolution hard copy text andgraphics. If you’re doing desktop publishing, presentation graphics, or anything elsethat requires top-grade or high-volume hard copy, you’ll want a laser printer. Ask somefriends for their opinions, and if printing is really important to you, don’t cut corners. Agood laser printer is the “geek’s” equivalent of a reliable truck.The modemThe term modem is a contraction of modulator/demodulator. A modem interfacesa computer to a telephone line, television cable system, fiber-optic network, or radiotransceiver, allowing you to communicate with other computer users and to “surf theInternet.”External versus internalAn external modem is a self-contained unit (box) that you can use with any com-puter. It has a cord that runs to the computer’s serial data port (also called the com-munications port) and another cord that runs to the telephone jack. The modemwill probably also have a jack into which you can plug your phone set.An internal modem is a printed-circuit board, also called a card, that is commonlyinstalled in new computers. Virtually all desktop computers come with modems. A newnotebook computer might not have an internal modem installed; in that case you canpurchase one in the form of a PC card that fits into a slot on the side of the computer.This card is roughly the height and width of a credit card, but somewhat thicker.Digital versus analogA computer works with binary digital signals, which are rapidly fluctuating directcurrents. For digital data to be conveyed over a telephone or radio circuit, the datamust be converted to analog form. In a telephone modem or radio-transceiver mo-dem, this is done by changing the digit 1 into an audio tone, and the digit 0 into an-other tone with a different pitch. The result is an extremely fast back-and-forthThe modem635