What is the primary purpose of a serial console cable?

The primary purpose of a serial console cable is to configure telephone and networking equipment. Such a cable typically connects to the console port of network devices, like routers and switches, allowing for direct communication with the device for both configuration and troubleshooting purposes. This is particularly useful when there is no network access or if the device is not functioning properly, enabling administrators to access device interfaces directly through a terminal or terminal emulation software.

Each of the other options does not appropriately represent the function of a serial console cable. Connecting external hard drives involves different connection types, such as USB or SATA. Transmitting video signals is usually handled by dedicated cables like HDMI or VGA, which serve a different purpose compared to the data-focused nature of serial console cables. Lastly, connecting printers typically requires parallel or USB connections, not serial connections, as modern printers do not typically use serial connections for data transfer.