A modem used to connect a computer to a cable TV service that provides Internet access. Cable modems can dramatically increase the bandwidth between the user's computer and the Internet service provider. Download speeds have reached 6 Mbps and beyond, but the connection is asynchronous. In order to prevent users with lower-cost cable access from hosting high-traffic Web servers, the upload speed is considerably slower, from 10 to 20 times slower. Cable operators also routinely change IP addresses assigned to users to prevent Web hosting .
Cable modems connect to the computer via an Ethernet port, which is an always-on connection. Ethernet is a shared medium, and the individual user's speed will vary depending on how many customers are sending or receiving data on that cable segment at the same time. For example, when the kids come home from school around 3pm, many cable users experience a corresponding slowdown. See DOCSIS, cable Internet, Internet appliance and MSN TV.
A cable modem is a special type of modem that is designed to modulate a data signal over cable television infrastructure. Cable modems are primarily used to deliver broadband Internet access, taking advantage of unused bandwidth on a cable television network. There were 22.5 million cable modem users in the United States during Q1 2005. That's up from 17.4 million in Q1 2004. It is also commonly found in Canada and Latin America.