A cable modem is a peripheral device used to connect to the Internet. It operates over coax cable TV lines and provides high-speed Internet access. Since cable modems offer an always-on connection and fast data transfer rates, they are considered broadband devices.
Dial-up modems, which were popular in the early years of the Internet, offered speeds close to 56 Kbps over analog telephone lines. Eventually, DSL and cable modems replaced dial-up modems since they offered much faster speeds. Early cable modems provided download and upload speeds of 1 to 3 Mbps, 20 to 60 times faster than the fastest dial-up modems. Today, standard cable Internet access speeds range from 25 to 50 Mbps. On the high end, Comcast offers an "Xfinity Extreme" service with speeds up to 505 Mbps.
Most cable modems include a standard RJ45 port that connects to the Ethernet port on your computer or router. Since most homes now have several Internet-enabled devices, cable modems are typically connected to home router, allowing multiple devices to access the Internet. Some cable modems even include a built-in wireless router, eliminating the need for a second device.
NOTE: While "cable modem" includes the word "modem," it does not function as a traditional modem (which is short for "modulator/demodulator"). Cable modems send and receive information digitally, so there is no need to modulate an analog signal.
Updated: March 29, 2014