What is the primary function of a modem in networking?

The primary function of a modem in networking is to allow computers to communicate over telephone lines. A modem, short for modulator-demodulator, facilitates the transmission of digital data over analog communication lines, such as traditional telephone lines. It converts digital data from a computer into analog signals that can travel over these lines and vice versa. This conversion is essential because the communication infrastructure, particularly in older systems, often relies on analog technology. This capability enables users to access the internet, send emails, and communicate over various online platforms using standard telephone connections.

The other options do not pertain to the primary function of a modem. For instance, enhancing storage capacity or graphics performance is related to hardware upgrades within the computer itself and not the role of a modem. Additionally, antivirus protection involves software designed to detect and eliminate malware, which is also outside the scope of modem functionality. Thus, the key aspect of a modem's role in networking is its ability to facilitate communication over various types of analog lines.