Which component is essential for connecting a server to external networks?

The Ethernet card is essential for connecting a server to external networks because it provides the necessary interface for the server to communicate over network protocols, facilitating data transmission. The Ethernet card, also known as a network interface card (NIC), allows the server to send and receive data packets over the Local Area Network (LAN) and wide area networks (WAN), including the internet. This connectivity is crucial for functions such as accessing resources on other servers, connecting to cloud services, and enabling remote management.

While power supply, hard drive, and cooling fan are all important components of a server, they do not directly facilitate network connectivity. The power supply provides electrical power to the server, the hard drive stores data and applications, and the cooling fan maintains optimal temperature within the server. However, none of these components enable the server to communicate with external networks, which is the primary function of the Ethernet card.