A modem is a piece of networking hardware that converts digital information into a signal that can be transmitted across the physical infrastructure of the Internet, and then decodes information received over the Internet back into a format understandable to a computer .
Modem is short for modulator-demodulator, and what a modem does is contained right in the name:
- Modulator: Computers store and send information in digital format. However, Internet connections made over phone lines or cables must be transmitted in a specific format. A modem serves as modulator when it encodes digital information into a format suitable for transmission over the Internet.
- Demodulator: When information is received over the Internet it must be decoded. A modem demodulates the signals received over cable and phone lines to decode the digital information that has been received.
When dial-up Internet connections were common, internal modems integrated into a computer were common. However, broadband modems, with integrated router functionality, are typically external devices and often supplied by an Internet Service Provider. The connection between the modem's integrated router and an Internet user's computer is usually made either with an Ethernet cable or wirelessly using WiFi.
Frequently Asked Questions
What's the difference between a modem and a router?
As we've just discussed, a modem is a device that establishes an Internet connection with an ISP over physical infrastructure such as a phone line or cable. While many modems include an integrated wireless router, a standalone modem without a router typically only includes a single Ethernet port which can be used to connect to the Internet.
A router cannot negotiate an Internet connection to an ISP without going through a modem. Instead, a router takes the Internet connection established by the modem and makes it accessible to more than one device at a time either by offering multiple Ethernet ports or by broadcasting the Internet connection as a WiFi signal.
Many modems today are modem-router combinations which can establish an Internet connection and then broadcast a WiFi signal. These types of devices are often supplied by an Internet Service Provider. However, wireless modems offering improved performance are also available from electronics retailers.
Why do I need a different modem for a DSL Internet connection than for a Cable Internet connection?
Phone lines, used to establish a DSL Internet connection, are used to carry information in the form of an electrical signal. Cables can be used to carry a signal using radio frequencies. Therefore, the signal emitted by a DSL modem and a cable modem are different to match the physical infrastructure over which the signal will be transmitted.