External modems are communication devices that computers utilize to connect to public networks like the Internet. A modem that sits inside the computer is called an internal modem, while modems that sit exterior, are external modems.
The type of modem you require depends on the type of Internet access service you desire. There are two general categories: Basic dial-up service, and high-speed broadband service.
Basic Dial-Up (Internal and External Modems)
Traditionally, internal modems have been dial-up modems that connect to Internet service providers (ISPs) using an analog signal over a telephone line. Since telephones also use analog signals, phones and modems cannot share lines simultaneously. Dial-up is the slowest, but also the least expensive way to connect to the Internet.
External modems can also be dial-up modems, and if so, will be rated at a transfer rate of 56 kbps (kilobytes per second), like their internal twins. They are handy when there are no available internal slots, or if the modem needs to be shared between computers that are not networked. In this case, an external modem connected to a desktop system can easily be disconnected and connected to a different desktop, or even a laptop.
External modems for dial-up service are inexpensive and available everywhere computers are sold. They are easy to setup, come with instructions, and most include fax capability at the software level. Recent versions of most operating systems recognize and load drivers for dial-up modems, which are plug-and-play devices.
High-speed Broadband Modems
Most external modems today are not dial-up modems, but broadband modems. Those designed for broadband service provide a different kind of Internet connection that is extremely fast, used with high-speed ISPs. Broadband modems typically have transfer rates from 1.5 — 8 mbps (megabytes per second), or higher.
DSL, FiOS, cable and satellite are different flavors of high-speed Internet. Normally ISPs selling broadband Internet access will provide their customers with external modems pre-configured to use with the service. Depending on the contract terms, the modems might be leased with a small monthly charge, or provided free to use for the duration of the client's contract. High-speed modems are normally not internal.
Broadband modems can be wired, or wireless. If wireless, a wireless network adapter must be installed in each computer that is to communicate with the modem. These adapters can be PCMCIA, or external devices that attach to the computer via the USB port.
DSL modems utilize the telephone line for sending digital signals rather than analog signals. Consequently, you can use the telephone while using DSL service. This is also true of FiOS service, which uses fiber optic lines in place of standard copper telephone lines. External modems used for high-speed cable service will not use the telephone line, but rather the cable TV line. Local cable companies provide cable Internet service, where available.