How A Network Interface Card Works
A Network Interface Card (aka NICaka Ethernet Adapter) is a device that enables a PC or othernetwork capable device to communicate with other PCs and devicesover a network. Any device, be it your PC, printer, broadbandmodem, home entertainment system or your refrigerator, thatneeds to communicate with other devices in your home must havea NIC to send and receive communication signals. (A modem isalso a device that sends and receives signals, but generallyspeaking it is for point to point communication rather thannetwork communication.)
Network interfaces are electronic hardware that handle the sending and receiving of signals. The can be built in to a device, add-on cards, or connected as an external device. They can also be wired or wireless. To be useful, a NIC must be connected to another device or devices equipped with a NIC.
Communication speeds currently available include 10, 100 and 1,000 megabits per second. A card may be labeled as 10baseT or 10/100 base TX, the number represents the speeds supported. Two PCs can communicate even if they have different ratings, they just will communicate at the rate supported by the slowest card.
A simple network might be comprised of two PCs in your home. Connected and configured for a local area network (LAN), those PCs would be able to transfer files to each other. Each PC can also share any connected devices, such as a printer. If PC "A" has a printer connected, it could share it and PC "B" could use it across the network to print. Similarly, if PC "A" can connect to the Internet, PC "B" can simultaneously share that connection to connect to the Internet.
A network interface uses a communication protocol, which is set of standards by which two devices agree on the format and structure of communications. An analogy would be in which two people agree to converse in English, only one person will speak at a time and they will speak not more than 25 words before giving the other person an opportunity to speak. Currently, the most commonly used protocol is TCP/IP (Transmission Control Protocol / Internet Protocol)
Once two devices agree on a protocol, they can begin communications. The manner in which they communicate is dictated by the protocol being used. Two devices using different protocols will not, generally, be able to communicate. This is why all PCs which will connect to the Internet must connect using TCP/IP. TCP/IP is the standard communication protocol for the Internet.