Dialup modems are called dialup because they use standard telephone lines to transmit and receive information. Dialup modems were the only kind of modems out there for years. A dialup modem can be
Internal: Typically part of the chipset on the motherboard, although many are also available as separate expansion cards (like in this figure). The advantage of an internal modem is that it doesn't take up any desk space, it uses the PC's internal power supply, and it's always on.
External: A boxy critter that sits on your desktop. It connects to the console via the serial port (traditional) or USB port, as shown in this figure. It also requires a separate power supply, which means that a typical external modem sports two more cables than its internal counterpart. The advantages of an external modem are that you can see its many pretty lights and you can manually turn the modem off when it acts stubborn.
Identical to both types of modem is the phone cord, which connects the modem to a phone jack on the wall. Many modems also provide a second phone cord jack into which you can plug a standard telephone (see this figure).
One advantage of a dialup modem is that you can use it anywhere you have telephone service. Simply plug the modem into the wall, and you can make phone calls with the computer just as you can make them yourself. Also, dialup is the least expensive way to get on the Internet.
The disadvantage of a dialup modem is that it’s painfully slow when compared to other ways of accessing the Internet.