Information Technology
Data Representation and Digital Logic
,Data Communication Devices
Modems
❖ In standard telephone service, a telephone converts the sound of your voice into an elect
signal that flows through die telephone wires.
❖ The telephone at the other end converts this electric signal back into sound so that t
person you are talking to can hear your voice.
❖ Both the sound wave and the telephone signal are analog signals, electrical waves th
vary continuously with the volume and pitch of the speakers' voices. A computer’s “voice"
digital; that is, it consists of on/off pulses representing Is and Os.
❖ A device called a modem is needed to translate these digital signals into analog signals that c
travel over standard telephone lines.
❖ In its modulation phase, the modem turns the computer’s digital signals into analog signals, whi
are then transmitted across the phone line.
,
, An external modem
❖ An external modem is a box that houses the modem's circuitry outside the
computer.
❖ It connects to the computer using a serial, USB, or FireWire port, and then connects
to the telephone system with a standard telephone jack.
An internal modem
❖ An internal modem is a circuit board that plugs into one of the computer's expansio
slots.
❖ An internal modem saves desktop space but occupies an expansion slot.
❖ Modems also come in the form of a PC Card for use with laptop computers and wit
newer models, are likely to be built into the laptop appearing as a port in one of th
sides.
Some use standard telephone lines, but others include a cellular phone, which
❖
enables completely wireless transmissions.
dems Fax mo
❖ Most modems used with personal computers also can emulate a fax machine.
❖ These devices can exchange faxes with any other fax modem or fax machine.
❖ With the proper software, users can convert incoming fax files into files that can
be edited with a word processor—something that stand-alone fax machines
cannot do.
Data Representation and Digital Logic
,Data Communication Devices
Modems
❖ In standard telephone service, a telephone converts the sound of your voice into an elect
signal that flows through die telephone wires.
❖ The telephone at the other end converts this electric signal back into sound so that t
person you are talking to can hear your voice.
❖ Both the sound wave and the telephone signal are analog signals, electrical waves th
vary continuously with the volume and pitch of the speakers' voices. A computer’s “voice"
digital; that is, it consists of on/off pulses representing Is and Os.
❖ A device called a modem is needed to translate these digital signals into analog signals that c
travel over standard telephone lines.
❖ In its modulation phase, the modem turns the computer’s digital signals into analog signals, whi
are then transmitted across the phone line.
,
, An external modem
❖ An external modem is a box that houses the modem's circuitry outside the
computer.
❖ It connects to the computer using a serial, USB, or FireWire port, and then connects
to the telephone system with a standard telephone jack.
An internal modem
❖ An internal modem is a circuit board that plugs into one of the computer's expansio
slots.
❖ An internal modem saves desktop space but occupies an expansion slot.
❖ Modems also come in the form of a PC Card for use with laptop computers and wit
newer models, are likely to be built into the laptop appearing as a port in one of th
sides.
Some use standard telephone lines, but others include a cellular phone, which
❖
enables completely wireless transmissions.
dems Fax mo
❖ Most modems used with personal computers also can emulate a fax machine.
❖ These devices can exchange faxes with any other fax modem or fax machine.
❖ With the proper software, users can convert incoming fax files into files that can
be edited with a word processor—something that stand-alone fax machines
cannot do.
