 1. Short for MODulator/DEModulator,
the first modem was first released by AT&T
in 1960 when it introduced its
dataphone. The modem is a
hardware device that enables a computer to
send and receive information over telephone lines. The modem is responsible for converting the digital data used by your computer into an analog signal used on phone lines and then converting
it back once received on the other end. To the right is an image of the UsRobotics 56k external Faxmodem, an example of what an external modem looks like.Because of the speed limitations of modems, many users are upgrading to a broadband connection such as a cable modem or DSL, which offer a faster download and upload speed when compared to the modem. Typical 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 would be transmitted over a phone line. In asynchronous communication, 1 byte (8 bits) is transferred within 1 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 10 bits. An example of what the above chart would transmit is the word HI which is equivalent to 2 bytes (16 bits).
Below are the three available types of modems that can be used in computers.
Internal modem that connects to a PCI slot inside
a newer desktop computer or ISA slot on an older
computer.
External modem is located within a box and is hooked up externally to the computer,
usually the Serial Ports or USB
port.
Removable modem that is used with older laptops
PCMCIA slot and is removed when you need the
PCMCIA slot for another device but are not planning on using the modem. 2. A
modem is also used to refer to the hardware device that connects a computer to a broadband network. Often this device is connected to the coaxial or other broadband line and a network cable or USB cable connects that device to the computer. Users may also connect the broadband modem to a router and allow multiple computers to share the connection.
- Additional information and help with computer modems can be found here.
- Additional information about installing a computer hardware including a modem can be found on document CHADD.
Also see: Connection, Dial-up, External modem, Modem definitions, Modulate, RJ-11, RTS, RXD | |
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