![]() ![]() ![]() One of the great benefits of using computers is that the stored data is easily accessible, and because computers make communications very easy the data stored on one computer can be transmitted to another one. Most computer applications, other than simple computer games, store data that can be used in the program. These lists may not have covered all the ways you have supplied data, but you can know with certainty where it all goes: straight to computer files.Īs computers have become widely used, protecting the privacy of data has become very important. And remember all the people who got your name and address from your check-fund-raisers, advertisers, and petitioners. There may be some forms you filled out with less delight-for taxes, military draft registration, a court petition,Īn insurance claim, or a stay in the hospital. Think about the forms you have willingly filled out: paperwork for loans or charge accounts, orders for merchandise through the mail, magazine subscription orders, applications for schools and jobs and clubs, and on and on. (c) In frequency modulation the amplitude of the wave stays the same but the frequency increases to indicate a 1 or stays the same to indicate a 0. As shown, the wave height is increased to represent a 1 or left the same to represent a 0. (b) The analog waveform can be converted to digital form through amplitude modulation. (a) An analog carrier wave moves up and down in a continuous cycle. An extra device is needed to make the conversions: a modem.įigure 1 Analog signals. Another characteristic that can be altered is the frequency, or number of times a wave repeats during a specific time interval frequency can be increased to represent a 1 (Figure 1c).Ĭonversion from digital to analog signals is called modulation, and the reverse process-reconstructing the original digital message at the other end of the transmission-is called demodulation. One such characteristic is the amplitude, or height of the wave, which can be increased to represent the binary number 1 (Figure 1b). It is converted by altering an analog signal, called a carrier wave, which has alterable characteristics (Figure 1a). To be sent over analog lines, a digital signal must first be converted to an analog form. Thus the most common communications devices all use analog transmission, a continuous electrical signal in the form of a wave. The easiest choice for most users is to piggyback (associated) on one of these. Communications devices such as telephone lines, coaxial cables, and microwave circuits are already in place for voice (analog) transmission. However, some communications media are not digital. Note, however, that the 56K speed is only for receiving data, and often not even that is up to full speed.ĭigital transmission sends data as distinct pulses, either on or off, in much the same way that data travels through the computer. The old-some very old-standard modem speeds of 9600, 14,400, 28,800, and 33,600 bits per second (bps) have now been superseded by modems that transmit 56,000 bps. This, and costs based on time use of services, provides strong incentives to transmit as quickly as possible. Modem Data Speeds The World Wide Web has given users an insatiable appetite for fast communications. PC cards have given portable computers full connectivity capability outside the constraints of an office. A cable runs from the PC card to the phone jack in the wall. The credit card¬sized PC card slides into a slot in the computer (Figure 4). Notebook and laptop computers often use modems that come in the form of PC cards, originally known as PCMCIA cards, named for the Personal Computer Memory Card International Association. For a modem that is out of sight-literally-an internal modem board can be inserted into the computer by the user in fact, most personal computers today come with an internal modem as standard equipment. Its main advantage is that it can be used with a variety of computers. An external modem is separate from the computer (Figure 3). A direct-connect modem is directly connected to the telephone line by means of a telephone jack. Most modems today are directly connected to the phone system by a cable that runs from the modem to the wall jack. Types of Modems Modems vary in the way they connect to the telephone line. ![]() A modem is a device that converts a digital signal to an analog signal and vice versa (Figure 2). ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |