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What is a Modem? What is the Purpose of a Modem? What are the Modem Parts?

written by: Tolga BALCI•edited by: Michele McDonough•updated: 5/27/2011

Modems are mysterious devices (as is the case for all computer hardware) that connect our computers to the Internet. In this article, we look at these devices in detail, beginning with what is a computer modem and what is its purpose, what does "modem" stand for, and what are its parts.

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    What is a Computer Modem? What does Modem Stand for? What is the Purpose of a Modem?

    D-Link Internal Modem The modem takes its name from the two functions it performs: modulator and demodulator, and this is basically the purpose of a modem. Modems change the analog signal to digital and the digital signal to analog.

    Let’s understand this modem definition with an example: Suppose that your computer makes a request from a website to view a webpage – something that we do everyday: we open up our web browser and connect to a website. The modem accepts the request in digital form from the computer, changes it to an analog signal (modulates it) so that it can be carried over the telephone wires and then sends it. When the request is answered, the answer reaches the modem in analog form, is converted to digital (demodulated), and sent to the computer. The conversion of the signals to/from analog to digital is the main purpose of a modem.

    You may wonder why there is a redundancy when converting analog and digital signals in both the computer and the other points in the Internet. The answer is simple – telephone lines are not able to carry digital signals and our computers can not understand anything other than 1s and 0s, the digital signals. So, there has to be something that can do this conversion and make every device understand the signals.

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    What are the Parts of a Modem?

    As it is an electronic device, there is a printed circuit inside the modem that holds the capacitors, resistors, transistors, amplifiers, regulators, flash memories, diodes, switches, and so on. For an overly technical view of the circuitry you can google a little and find very useful (and possibly overwhelming) results. For the purposes of this article, we will stick with the basic conceptual components of modems.

    US Robotics External Modem Modems have the parts to send and receive signals (digital and analog) and to convert them to one another. In an internal dial-up modem, sending and receiving is done by the connection of the telephone line and the signals are sent to the computer via the motherboard connection. In external modems, sending and receiving is done again by the telephone line connection and the signals are sent to the computer via the serial or USB port. In broadband modems (known as the DSL modems), the sending and receiving component is the same, however the signals are sent to the computer through the Ethernet or the USB connection (I recommend using one with an Ethernet connection). If the modem can transmit and receive data at the same time, it is called a “duplex" modem. If not, it is called a “simplex" modem.

    In processing the signals, the modem has a flash memory that holds the operating system, which consists of the set of instructions on how to process the signals and transfer them to the connection – the connection being either the telephone line connection or the connection with the computer. Since we are talking on an “operating system", there is a central processing unit and memory.

    Modulation and demodulation is done by separate parts – the modulator and the demodulator as you have guessed. Assuming that the data packets that arrive and sent from the computer can contain errors, there is also an error control module on the modem.

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    Softmodems (Winmodems or Dumb Modems)

    Softmodems evolved from the simple idea of transferring the hardware tasks of the modem to the computer’s operating system. So, the modem is only a piece of hardware that is a simple digital signal processor; the modulation and the demodulation is done on the computer side. The application of the idea reduced the cost of the modem by using less hardware components. However, the modulation and the demodulation process was done by using the computer’s resources, resulting in overall performance slowdowns. Moreover, the modems may not be usable (as often is the case) with other operating systems or other Windows versions, because the drivers are simply not available. What is more, the driver software or the operating system’s library may fail and leave the system with freeze or instability, together with the happy exploitation of the software by the bad guys on the Internet. A friend of mine sadly experienced this when he downloaded the drivers for his softmodem from the Internet, which were, in fact, altered to contain a virus.

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    Wireless Modems, Mobile Modems (GSM Modems, 3G USB Modems)

    Motorola IM 1100 Wireless Laptop Modem Yesterday’s technology was to send and receive analog and digital signals in compressed form, both on the modem and the Internet Service Provider's side, to increase speed. Today’s technology is connecting to the Internet from wireless access points and from mobile devices. The wireless modems can be together with a router or one device that can have both modem and router functions. Modern wireless devices also have connection-sharing capability. That means, a wireless modem/router on your desktop lets you share your Internet connection with your family members. A wireless modem (as you see on the left) can establish a wireless connection with another computer, given that the other computer also has a wireless modem (by the way, this is called an ad-hoc network. If you like the idea, you can see how you can set an ad-hoc network using Windows XP or Windows 7.)

    Mobile modems (also called GSM modems) are simple and the basic functionality is the same, they provide you a broadband connection, that is mobile. Most common GSM modems are 3G modems in Europe and recently 4G modems in United States. The 3G USB modems are the most common GSM modems types you can see nowadays and they are very cheap to own (especially with a contract from your wireless carrier.) As the name says, the 3G USB modems are connected to the computer via the USB interface and contains a SIM card, which connects the GSM modem to the GSM network. Since these hi-tech 3G USB modems are basically "modems", they modulate and demodulate the computer signals, but this time not over the conventional telephone line, but over the modern wireless line.

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    Conclusion

    The main purpose and function of a modem is converting analog and digital signals to/from each other. There can be additional functions as we have just described above or the transmit/receive speeds can be increased, as in the case of broadband modems.

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    References

    Article: Author's own experience

    Screenshots

    1. D-Link Internal Modem: http://www.dlink.com
    2. Actiontec External Modem: http://alatest.com/reviews/modem-reviews/actiontec-usb-serial-56k-external-modem/po3-36872491,99/
    3. Motorola Wireless Modem: http://www.ctssales.com/im1100.asp