The most common NIC we find on X399 motherboards is the Intel i211AT, which is a Gbit Ethernet controller. Some motherboards have two (on the left) of these NICs. The Killer E2500 can also be found on X399 boards, and it's marketed more towards gamers, but does fine as a normal NIC.
A nice treat can be found on some X399 motherboards, the new Aquantia 10Gbit NBase-T controller (AQC107). NBase-T allows for 10G, 5G, 2.5G, 1G, and 100M link speeds and will have you covered for future upgrades in the network arena if you don't already have a 10Gbit network. ASUS's XG-U2008 switch offers two 10G ports for $220, bringing 10G networking into the mainstream. I am told 2.5G and 5G will become much more common next year in affordable routers and switches.
While one vendor integrated the chip into the motherboard, another chose to put it on an x4 PCI-E card. The benefit of having it integrated means you can fill up all PCI-E slots, but you can't take it with you. The benefit of having it on a card is that you can use it in another system, but you can't fill up the PCI-E slots.
We also find some wireless AC solutions, and the most common so far is the Intel 8265NGW 2x2 (867Mbps) Wireless AC card. We find it built into the motherboard through an M.2 slot wired for WIFI cards and output on the rear IO, and we also find it on an add-in card included with an X399 motherboard. You can take both with you, since both ways it plugs into an M.2 slot wired for WIFI/BT.
One vendor has gone above and beyond and implemented a Wireless AD (WiGig) card, the Qualcomm QCA9008, which is capable of up to 4.6Gbps (yea you read that right). The card also supports 2x2 Wireless AC and the other Wireless technologies below it. Wireless AD is super-fast, but it has to have a clear line of sight, and its main use is for future wireless VR headsets. I also spotted an Intel Wireless AC 3168NGW card, but it's half the speed as the other Intel cards I found on other motherboards at 433Mbps (1x1).
Some vendors have gone to lengths to improve audio, and some have gold plated audio ports on their motherboards as well, such as the vendor pictured above. You can also see the triple NICs, one of those is a 10G, and the other is 1G.
The basic audio solution found on X399 motherboards is a single ALC1220 audio codec. The codec offers 120dB SNR on one output, along with a single integrated headphone amplifier, some vendors add a second amplifier, so the rear and front panel audio output are both amplified (vendor on the right). One vendor has even added in an extra digital to audio converter (DAC), the ESS Sabre ESS9018, which should greatly improve audio. Vendors also implement physical PCB division and audio capacitors.
The vendor pictured above has actually implemented two front panel HD audio outputs. They are wired to the same output, and you can use one or the other, but the reason for their existence is for cable management. If you have a card in the last slot, it could block the front-facing port, but if you have a very short case, the bottom facing output could be blocked, so the vendor includes both types.
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