Modem:

Combined device for modulation and demodulation.

Modulation:

Strengthen signal for transmitting long distance.

Demodulation:

Used to recover the content of original information.

What is modem for computer?

Enables computer to transmit data over telephone or cable lines.


How information is transmitted over telephone line?

Information is stored digitally but while travelling it will be sent in form of analog waves.

Analog waves:

Continuous waves that vary in strength and quality.

Why data is to represented in signal? 

Signal is physical representation of data.

Who invented computer Modem?

Dennis Hayes and Dale Heatherington.

Features of Modem:

Speed.
Auto answering.
Self testing.
Voice over data.
Auto dial/Redial.

Self testing:

Test digital connection to terminal and analog connection to remote modem.

Internal Modem:

Internally to communicate with other computers.


Advantages:

Less cost.
Already installed in CPU.
Efficient place.

Disadvantages:

Increase in CPU temperature.
Difficult to identify status.

External Modem:

Own power supply.
Turn off modem to break online connection.

Advantages:

Easily removed.
Status light.

Disadvantages:

Expensive.
Separate place.

PC card Modem:

Plugged directly external slot of PC.