How a Modem Works


Tutorial Home >Hardware >Components >Modems >How do I understand how a modem sends and receives data on my computer?
Tutorial Home >Hardware >Components >Modems >Installing a Modem >How a Modem Works

  Step 1:  External Modem

An external modem plugs into a serial port on the back of the computer. It gets its power from an AC adapter that plugs into an electrical outlet. Your modem will attach to either a 25-pin or a 9-pin serial port. Adapters/gender changers are available if your modem cable does not match the PC connection.
  Step 2:  Internal Modem

An internal modem is installed on an empty slot on a computer's motherboard. It has its own serial port, so it need not be connected to an existing one on the PC. It draws its power from the motherboard.
  Step 3:  Phone Line

The phone line plugs into the jack on the back of the modem and connects the modem to the phone system. You can connect the modem directly to the phone system without a telephone by connecting the line directly to the line jack.
  Step 4:  Phone Jack

The phone jack is a second connector on the back of the modem. By plugging a telephone into this jack, and then plugging the line jack into the phone jack on your wall, you are able to use your telephone when you're not using your modem.
  Step 5:  Serial Port

Data is sent and received from the computer via the serial port, through the modem, and then onto the phone lines.
  Step 6:  Data

Your computer works with digital data—binary bits of information that are either on or off. The telephone system, on the other hand, works with analog information—streams of continuous electric current that vary in frequency and strength. When you send information from your modem to another modem—such as on the Internet—the digital data in your computer has to be changed to analog information so it can be sent via the telephone system. The computer sends digital information to the modem, which changes it—modulates it—into analog signals.
  Step 7:  MODEM

The analog signals travel over the phone system and are received by another modem where they are changed by the receiving modem—demodulated—from analog data back to digital data, and sent into the computer via the serial port. This modulating and demodulating of data is what gives the modem its name; MOodulatingDEModulating.