Modems convert the digital data signal created by your computer into an analog sound so that the signal may be transmitted over conventional telephone lines.
Modems can be external or internal, however internal modems are more common in PCs than in Macs.
Hayes Company was one of the first to manufacture modems for use with desktop computers. Hayes compatibility is an important feature to look for when shopping for a modem. This is the modem's maximum data transfer rate. Baud rate is another term associated with modem speed. In order for two modems to communicate with each other they must support a common data transfer rate.