Definition

• Modem stands for modulator-demodulator. The characteristics of a carrier signal are modulated to pass information to a computer.
  
  

Modulation, Demodulation

• When the demodulator part of the modem detects that the carrier signal has changed, it will get ready to receive data. During modulation, the carrier is changed to impart information. During demodulation, the signal is interpreted.
  
  

Internal vs. External

• External modems are peripherals, i.e., they attach to the outside of a computer by way of a USB or serial port, or even by infrared. Internal modems are built into the computer's motherboard.
  
  

Implementation

• Internal modems may be added into a slot on the desktop computer motherboard, or on a laptop may slide in as a PCMCIA card. Internal modems are typically already installed on new desktop computers.
  
  

Drivers

• Internal modems require drivers to make them work because they are not a fundamental part of the computer, and thus the computer must be told how to run them.