Ethernet Cards and Network Adapters

Slot first: PCIe lanes, legacy PCI and USB

Choose by the slot you have free. Most current cards are PCI Express and come in x1, x4 and x8 lengths; a shorter card fits a longer slot, and a 10 Gbit card needs enough lanes, such as x4 or x8, to reach full speed. Older machines may still use 32-bit PCI, a different connector altogether. Laptops and small PCs use a USB adapter or a Mini PCIe card instead. Check the bracket too: a low-profile case needs a low-profile bracket.

Speed, ports and cabling: RJ45 or SFP+

Gigabit is the baseline, 2.5 Gbit works over ordinary Cat5e, and 10 Gbit needs Cat6a for full distance or shorter runs of Cat6. Dual and quad-port cards suit servers, firewalls and virtual machines. SFP+ cages take optical modules or copper direct-attach cables instead of RJ45 twisted pair. The card only runs at the speed your switch and cable allow, so a 10 Gbit card on a gigabit switch drops to 1 Gbit. Check driver support for your operating system, especially Linux and virtualization hosts.

Questions about Ethernet Cards and Network Adapters

Will a PCIe x4 card work in an x16 slot?

Yes. A shorter PCI Express card fits a longer slot and uses only the lanes it has. The reverse works only if the slot is open-ended, and then the card runs with fewer lanes.

Do I need a separate network card if my motherboard has Ethernet?

Not usually. Add one for more ports, a faster speed such as 10 Gbit, SFP+ fiber, or features your onboard chip lacks. A card is also a quick fix if the built-in port fails or lacks a driver for your operating system.

Which cable do I need for 10 gigabit over copper?

Cat6a handles 10GBASE-T to the full 100 meters. Cat6 works up to about 55 meters, depending on the environment, and Cat5e is meant for 1 Gbit and 2.5 Gbit. For a short rack link, direct-attach cables on SFP+ ports are an option.