Modem

Updated: 08/02/2020 by Computer Hope

A modem may refer to any of the following:

Cable modem

1. A modem or broadband modem is a hardware device that connects a computer or router to a broadband network. For example, a cable modem and DSL modem are two examples of these types of Modems.

Tip

Today, a "modem" is most often used to describe a broadband modem. However, it also describes what was initially considered a modem (described below) to connect to the Internet. To help prevent confusion, use the terms "broadband modem" and "dial-up modem."

Note

A broadband modem is an external device that connects to your computers and other network devices using either a network cable or over a wireless connection.

2. Short for modulator/demodulator, a modem is a hardware device that allows a computer to send and receive information over telephone lines. When sending a signal, the device converts ("modulates") digital data to an analog audio signal, and transmits it over a telephone line. Similarly, when an analog signal is received, the modem converts it back ("demodulates" it) to a digital signal.

Tip

To help prevent confusion between a broadband modem, you can refer to this modem as a dial-up modem.

The picture below is an example of an internal expansion card dial-up modem. Click the image to get a description of each component on the card.

Internal modem

Modems are referred to as an asynchronous device, meaning that the device transmits data in an intermittent stream of small packets. Once received, the receiving system then takes the data in the packets and reassembles it into a form the computer can use.

Stop
1 bit
Data
8 bits
Start
1 bit
Stop
1 bit
Data
8 bits
Start
1 bit
Packet
10 bits
Packet
10 bits

The above chart represents how an asynchronous transmission transmits over a phone line. In asynchronous communication, one byte (eight bits) is transferred within one packet, which is equivalent to one character. However, for the computer to receive this information, each packet must contain a Start and a Stop bit; therefore, the complete packet would be ten bits. The above chart is a transmission of the word HI, which is equivalent to two bytes (16 bits).

History of the modem

The first modem, known as the Dataphone, was released by AT&T in 1960. It later became more common for home users when Dennis Hayes and Dale Heatherington released the 80-103A modem in 1977.

Dial-up modems were commonly used by computers to connect to the Internet through the early 2000s until broadband Internet started to be more widely available. As broadband Internet became available and popular, dial-up modems were used by fewer computer users. Today, computers no longer come with a dial-up modem, requiring users who need one to purchase and install it.

What does a modem sound like?

If you did not grow up on a dial-up modem or you're nostalgic, you can listen to a modem connecting to the Internet in the sound file below. Each time someone connected to the Internet, they heard these noises over the modem speaker.

In this audio file, you hear the modem dialing a phone number and then communicating with the other modem over the phone line. The squealing noise heard after the phone number is the modem establishing a connection (handshaking). When the connection is established, the modem goes silent.

Why does a modem need to make this noise?

The computer uses a digital signal. However, a phone line that was designed for voices uses an analog signal. The modem makes these noises and tones to transmit digital information over an analog line.

Types of computer modems

Below are the four versions of a computer modem found in computers.

Onboard modem - Modem built onto the computer motherboard. These modems cannot be removed, but can be disabled through a jumper or BIOS setup.

Internal modem - Modem that connects to a PCI slot inside a newer desktop computer, or ISA slot on an older computer. The internal modem shown above is an example of a PCI modem.

External computer modem

External modem - Modem in a box that connects to the computer externally, using a serial port or USB port. The picture is an example of an external USRobotics modem.

Removable modem - Modem used with older laptops PCMCIA slot and can be added or removed as needed.

What are the speeds of modems?

Modem speed is measured in bps and Kbps, which is the speed the modem can send and receive data. Today, a 56 K (56,000 bps) modem is the fastest solution and speed used with today's dial-up modem.

Note

The line quality that the phone communicates over, and how many collocations it must use, also affects the speed of a modem. Although a modem may be rated as 56 K, if the line quality and collocations are not optimal, you cannot achieve the maximum speed. Also, when a modem establishes a connection to another modem not using the same standard or a lower speed, the lowest speed is used.

Earlier speeds of modems included 110 baud, 300 baud, 1200 baud, 2400 baud, 4800 baud, 9600 baud, 14.4k, 28.8k, and 33.6k.

Modem features and standards

A modem may also include some or all of the features and specifications listed below.

  • Auto-answer - A modem's ability to automatically answer the phone after the phone rings a set amount of time.
  • Data/Voice - Modems with voice capability that switch between a voice and data communication.
  • Fax - Fax modems can send and receive a fax with the proper software.
  • V.90 - The standard that the modem uses also allows it to communicate at an optimal speed. When first introduced, there were multiple standards, but nearly all 56 K modems use the V.90 standard.

Why is a modem an input and output device?

A Modem is considered an input and output device because it sends data (upload/output) and receives data (download/input).

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