What type of cable is commonly used to connect serial devices such as modems?

The use of a Serial Cable, particularly a DB9 cable, is standard for connecting serial devices such as modems. This type of cable features a 9-pin connector commonly used in RS-232 serial communication. The DB9 connection allows for a direct interface to the serial ports of various devices, enabling communication for configuration, data transfer, and other serial-based protocols.

In contrast, a USB cable is mainly used for connecting modern peripherals, offering faster speeds and plug-and-play capabilities, which is not typically compatible with older serial devices. RJ45 cables are specifically designed for Ethernet networking and are not suitable for serial connections. HDMI cables, on the other hand, are used for transmitting high-definition video and audio signals, and they do not serve a purpose in connecting serial devices. Thus, the use of a Serial Cable is the most appropriate choice for connecting devices like modems that rely on serial communication standards.