Modem

Diagram of a modem connection between the network and the user's PC.

(m dem) (n.) Short for modulator-demodulator. A modem is a device or program that enables a computer to transmit data over, for example, telephone or cable lines. Computer information is stored digitally, whereas information transmitted over telephone lines is transmitted in the form of analog waves. A modem converts between these two forms.

Standard Modem Interface

The USB standard has largely replaced RS-232 in both telephone and cable modems. and

Early telelphone modems used a standard interface for connecting external modems to computers called RS-232. Consequently, any external modem can be attached to any computer that has an RS-232 port, which almost all personal computers have. There are also modems that come as an expansion board that you can insert into a vacant expansion slot in your PC. These are sometimes called onboard or internal modems.

Protocols for Formatting Data

While the modem interfaces are standardized, a number of different protocols for formatting data to be transmitted over telephone lines exist. Some, like CCITT V.34, are official standards, while others have been developed by private companies. Most modems have built-in supportfor the more common protocols — at slow data transmission speeds at least, most modems can communicate with each other. At high transmission speeds, however, the protocols are less standardized.

Aside from the transmission protocols that they support, the following characteristics distinguish one modem from another:

  • bps : How fast the modem can transmit and receive data. At slow rates, modems are measured in terms of baud rates. The slowest rate is 300 baud (about 25 cps). At higher speeds, modems are measured in terms of bits per second (bps). The fastest modems run at 57,600 bps, although they can achieve even higher data transfer ratesby compressing the data. Obviously, the faster the transmission rate, the faster you can send and receive data. Note, however, that you cannot receive data any faster than it is being sent. If, for example, the device sending data to your computer is sending it at 2,400 bps, you must receive it at 2,400 bps. It does not always pay, therefore, to have a very fast modem. In addition, some telephone lines are unable to transmit data reliably at very high rates.
  • voice/data: Many modems support a switch to change between voice and data modes. In data mode, the modem acts like a regular modem. In voice mode, the modem acts like a regular telephone. Modems that support a voice/data switch have a built-in loudspeaker and microphone for voice communication.
  • auto-answer :An auto-answer modem enables your computer to receive calls in your absence. This is only necessary if you are offering some type of computer service that people can call in to use.
  • data compression :Some modems perform data compression, which enables them to send data at faster rates. However, the modem at the receiving end must be able to decompress the data using the same compression technique.
  • flash memory : Some modems come with flash memory rather than conventional ROM, which means that the communications protocolscan be easily updated if necessary.
  • fax capability: Most modern modems are fax modems, which means that they can send and receive faxes.
  • To get the most out of a modem, you should have a communications software package,a program that simplifies the task of transferring data.

    See “Dial-Up Modem Standards” and “Types of Internet Connections” in the Quick Reference section of Webopedia.

    UPDATED: This article was updated April 2021 by Web Webster.

     

     

     

    Vangie Beal
    Vangie Beal is a freelance business and technology writer covering Internet technologies and online business since the late '90s.

    Top Articles

    The Complete List of 1500+ Common Text Abbreviations & Acronyms

    From A3 to ZZZ we list 1,559 SMS, online chat, and text abbreviations to help you translate and understand today's texting lingo. Includes Top...

    Windows Operating System History & Versions

    The Windows operating system (Windows OS) refers to a family of operating systems developed by Microsoft Corporation. We look at the history of Windows...

    How to Create a Website Shortcut on Your Desktop

    Website Shortcut on Your Desktop reviewed by Web Webster   This Webopedia guide will show you how to create a website shortcut on your desktop using...

    Generations of Computers (1st to 5th)

    Reviewed by Web Webster Learn about each of the 5 generations of computers and major technology developments that have led to the computing devices that...

    SAP Software

    SAP is an end-to-end enterprise solution provider specializing in enterprise resource...

    Chief Operating Officer (COO)

    The chief operating officer (COO) is a member of a company's senior executive...

    Kanban

    Kanban is a workflow management method intended to define, manage, and improve services...