A modem is an communication device which allows your computer to communicate with other computers over a communications link. The modem's job is to convert your data into the format used on the communications connection and the remote modem converts that transmission back into data. Examples of modems include a standard fax/phone modem, a cable modem or a DSL modem or even a satellite modem. All modems perform what is called modulation to encode your data into the line signal and demodulation to decode it from the line signal. The term MODEM is short for Modulator/Demodulator.

Modems come in many shapes and sizes but can be generally broken down into two categories, internal and external. As the names imply, an internal modem goes inside your computer into either an ISA or PCI slot. External modems are attached to the computer through some other connection but are physically outside the computer case.


  1. External
  2. Internal
    1. ISA
    2. PCI


  1. Standard Analog (phone/voice/fax)
  2. ISDN modems
  3. Digital cable modems
  4. xDSL modems
  5. Satellite


  1. Modulation/Demodulation
  2. Error Correction
  3. Compression/Decompression


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