Some cards can support multiple protocols or multiple media. For example, you can get cards that have both RJ-45 and BNC ports for either twisted pair or thin coax cable. Some PCs come with NICs built-in but most require the addition of a card using either an ISA or PCI expansion slot. What you choose will be dictated by the type of expansion slots you have available. The PCI interface is more efficient, but older computers may not have free PCI slots.
Laptops can use NICs that fit into the PC card slot.
Ordinarily, the speed of the NIC should match the LAN speed, but it's possible to connect a computer with a 10 Mbps card to a 100 Mbps network. NICs also have different bus widths which determine how much data can be transferred to and from your computer at one time. The greater the bus width the better. The adapter attaches to a computer's USB port on one end and an ethernet cable on the other. However, the adapter can only transfer data at 4 Mbps which doesn't take advantage of the full networking speed of ethernet.