Historically, NICs were separate expansion cards, but in modern computers, they are often integrated into the motherboard. 

• Connectivity: NICs provide the physical interface for a computer to connect to a network, typically using Ethernet for wired networks or Wi-Fi for wireless connections.

• Data Transmission: The primary function of a NIC is to transmit and receive data over a network. It converts data from the computer into a format that can be transmitted over the network and vice versa.

• MAC Address: Each NIC has a unique Media Access Control (MAC) address, which identifies the device on the network. This address is used for directing network traffic to and from the NIC.

• Types of Networks: NICs can connect a computer to various types of networks, including local area networks (LANs), wide area networks (WANs), and the internet.

• Speed and Duplex Settings: NICs have different speed capabilities (such as 10/100/1000 Mbps) and can operate in either half-duplex or full-duplex mode, affecting the data transmission rate and efficiency.

Network Interface Cards are essential components in networking, providing the necessary hardware interface for computers and other devices to communicate over networks.