Ethernet Card (NIC)

A computer is built to work with numbers inside its own case. A network cable carries electrical signals to somewhere else. Something has to stand in between and turn one into the other. That is the Ethernet card.

1What an Ethernet card is

Ethernet card

An Ethernet card is a piece of hardware that connects a computer to a wired network. It is also called a network interface card (NIC) or a network adapter. Every NIC has an RJ45 port for the network cable, and every NIC bears its own unique MAC address.

Ethernet is the name of the most common way of wiring a LAN, which is where the card gets its name. Build one below, step by step.

Fit an Ethernet card

Go through the four steps. Drag sideways to turn the card.

An Ethernet card: a small circuit board with an RJ45 port for the network cable (Ethernet cable / LAN wire), a chip that sends and receives, and gold contacts that plug into the computer.

2What it does

🔌 Gives the cable a port

The RJ45 port on the card is the opening that takes the RJ45 plug of a network cable (Ethernet cable / LAN wire).

🔁 Sends and receives

It turns the computer’s data into signals on the cable, and signals from the cable back into data.

🏷️ Bears a MAC address

Every NIC bears its own MAC address, fixed when it is made, so the network can tell one computer from another.

A card can be a separate board plugged into a slot, as in the lab. In most computers and laptops made today, the same chip and RJ45 port are built straight onto the motherboard instead. It is still called a network card; it just is not a separate card any more.

3The MAC address

MAC address

A MAC address (Media Access Control address) is a unique number that every NIC (network card) bears, given to it when it is made. It is written as six pairs of hexadecimal digits, like 00:1A:2B:3C:4D:5E.

Hexadecimal digits are the ten digits 0–9 and the six letters A–F, which is why letters appear in the address. Think of a MAC address like the chassis number stamped on a car. It stays with the card for its whole life, wherever the computer is taken. The first three pairs tell you which company made the card; the last three are that company’s number for this one card.

Why this matters later

A switch uses MAC addresses to send data only to the computer it is meant for. You will see it do that in the Switch lesson. A different kind of address, the IP address, is covered in Data Communication.

4How fast is it?

The speed of a card is measured in bits per second — how many 1s and 0s it can send in one second. Ethernet cards range from 10 Mbps (ten million bits per second) up to 1 Gbps (a thousand million) in most computers, and faster ones exist for servers.

5Check yourself

Quick Check

Which of these is another name for an Ethernet card?

Quick Check

What is a MAC address?

Quick Check

How many pairs of digits make up a MAC address?

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RJ45 Connector 🔌