A network card (also called a network adapter, network interface card, or NIC for short) acts as the interface between a computer and a network cable. The purpose of the network card is to prepare, send, and control data on the network. In this article we will introduce this component.
A network card usually has two indicator lights (LEDs):
The orange (10 Mb/s) or red (100 Mb/s) LED indicates network activity (sending or receiving data).
To prepare data to be sent the network card uses a transceiver, which transforms parallel data into serial data. Each card has a unique address, called a MAC address, assigned by the manufacturer, which lets it be uniquely identified among all the network cards in the world.
Network cards have settings which can be configured. Among them are hardware interrupts (IRQ), the I/O address and the memory address (DMA).
To ensure that the computer and network are compatible, the card must be suitable for the computer's data bus architecture, and have the appropriate type of socket for the cable. Each card is designed to work with a certain kind of cable. Some cards include multiple interface connectors (which can be configured using jumpers, DIP switches, or software). The most commonly used are RJ-45 connectors.
Note: Certain proprietary network topologies which use twisted pair cables employ RJ-11connectors. These topologies are sometimes called pre-10BaseT .
Finally, to ensure that the computer and network are compatible, the card must be compatible with the computer's internal structure (data bus architecture) and have a connector suitable for the kind of cabling used.
A network card is the physical interface between the computer and cable. It converts the data sent by the computer into a form which can be used by the network cable, transfers that data to another computer and controls the data flow between the computer and cable. It also translates the data coming from the cable into bytes so that the computer's CPU can read it. This is why a network card is an expansion card inserted into an expansion slot.
The paths taken by data moving with a computer are called buses. Multiple side-by-side paths force data to move in parallel, and not in series (one after another).
The computer and the card must communicate so that data can travel between them. For this reason, the computer assigns part of its memory to cards that include DMA (Direct Access Memory).
The interface card indicates that another computer is requesting data from that computer.
The computer's bus transfers the data from the computer memory to the network card.
If the data is moving too fast for the adapter to process, they are placed in the card's buffer memory (RAM), where they are temporarily stored while the data is being sent and received.
Before the sending network card transmits its data, it interacts electronically with the receiving card to resolve the following issues:
Data transmission speed: if a more recent and advanced card communicates with a older one, they still have to share the same transmission speed. Some cards have circuits for adjusting themselves to the transfer speeds of a slower card. Both cards must accept and adjust to the other card's settings before data can be sent and received.
Network adapters have a configuration options, among others:
Interruption (IRQ): In most cases, network cards use IRQ 3 and 5. IRQ 5 is recommended (whenever available) and most cards use it as the default setting.
Input/Output (I/O) base address: Each device must have a different address for the corresponding port.
Memory address: This designates a RAM location in the computer. The network card uses this slot as a buffer for data entering and leaving. This setting is sometimes called the RAM Start Address. In general, a network card's memory address is D8000. The last 0 is left out on some network cards. You have to be careful not to select an address already being used by another device. It should, however, be noted that some network cards have no configurable memory address because they don't use the machine's RAM addresses.
Note: The card can be configured using software. The settings have to match the placement of the jumpers or the DIP (Dual Inline Package) switches found on the network card. These settings are provided with the card's documentation. Many recent cards use PnP (Plug and Play). This means that the card does not need to be manually configured, but sometimes can cause hardware conflicts; when this happens, it is helpful to disable the PnP option and configure the card "by hand."
Image: © Everypixel