- PCMCIA interfacepc card insertion end image by Georgios Alexandris from Fotolia.com
The form factor of a card means how the card connects to a computer. Originally, an Ethernet card was installed inside the machine and connected to the bus of the computer. The first type of card connected to the ISA bus. This was soon replaced by PCI bus cards. These can still be used to add additional Ethernet ports to desktop machines or servers. The next type of interface was a PCIMCA card that would slide into a slot in the side of a laptop. Now USB-attached interfaces are common. These cards are available for both Ethernet and Wi-Fi. The operation of both Ethernet and Wi-Fi cards is similar, although not identical. - Twisted pair interfaces are common today.ethernet image by MATTHIEU FABISIAK from Fotolia.com
The Ethernet interface connects directly to the network. In the 1980s Ethernet cards had coaxial cable connectors on the card. Through the late 1980s and early 1990s almost all coaxial cable wiring systems were replaced by twisted pair wiring. After 2000 almost all Ethernet cards or interfaces had twisted pair interfaces. - Cards respond to their own addresses.address image by Aleksander from Fotolia.com
The card manufacturer assigns a unique address to each Ethernet interface. This is called the Built In Address or BIA. The Ethernet interface listens to frames on the Local Area Network. If the destination address matches one of selected addresses for the card, the frame is buffered and the card generates a CPU interrupt. Then the host software processes the frame. Normally the card will select frames with the BIA or the broadcast address. Broadcast frames are used to perform important maintenance functions. All nodes on a LAN are required to read and process broadcast frames. - Multicast allows groups to be selected.Multiple colored straws. image by Saskia Massink from Fotolia.com
Multicast frames are sent onto the LAN with the intention of allowing endpoints to read them, but not requiring the endpoints to read them. Multicast address are identified by a special bit in the address field. Each multicast group is identified by the remaining bits in the address field. Host software can register multicast addresses with the Ethernet card. The Ethernet card will then read, buffer and generate a CPU interrupt for any frames with that multicast group destination address. - Promiscuous mode selects all traffic.sign. all traffic. access for all traffic image by L. Shat from Fotolia.com
Host software can also set a card into promiscuous mode. Promiscuous means it is not selective. In promiscuous mode the card reads, buffers and generates a CPU interrupt for all frames that it receives. This gives the host software access to every frame on the LAN. This is a useful debugging tool, but it can also be used by crackers to get unauthorized access to information. Software access to the card is provided by a standard Application Program Interface, or API.
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