Modem is short form for "demodulator/modulator". A modem allows a computer to send or receive data through a connection. It works by changing the regular analog signal to a digital signal to be used by computers. Different types of modems exist such as dial-up, cable, DSL, and wireless.
Standard Dial-up - These modems have the slowest transfer speed (downloads) of all modems. Dial-up modems are capable of speeds of up to 56 kilobits per second through an Internet Service Provider connection. Dial-up modems use phone lines to connect with the Internet.
DSL (Digital Subscriber Line) - DSL is also provided through regular copper lines though it is not available to everyone, since you have to be close to a telephone switching office (usually within about 4 miles). DSL speeds can differ depending on the quality of the connection. Still, download speeds typically will be about 1000 kilobits per second on a good connection.
Cable Modem - A cable modem runs over cable television lines. The coaxial cable it uses gives you much more bandwidth than dial-up and therefore gives you extremely fast access to the World Wide Web. These modems can give you a transmission rate of about 2000 kilobits per second which is about 40 times faster than the top speed of dial-up! However, speeds may vary depending on the location or other concerns.
Wireless Broadband Internet - Wireless Internet (Wi-fi) connects using radio frequency signals, rather than phone lines or cable television lines. Also, you can connect to the internet within a limited range, which means an equipped laptop can connect to the internet away from home easily when a "Hotspot" is available. Wireless Internet is popular in PDAs, cellular phones, and other portable devices including laptops and notebooks. Download speeds of Wireless Internet can sometimes reach about 1.5 megabits (almost 2 million kilobits), much faster than other connections.