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I'm looking at motherboards and I'm debating on spending more for one with built-in Wi-Fi. I was wondering how this is presented to the OS. I'd like to use PCI pass-through, so I'm wondering if it uses PCI somehow or some other technology like USB.

The specific motherboard I'm looking at is the MSI z370 gaming carbon AC

https://www.msi.com/Motherboard/Z370-GAMING-PRO-CARBON-AC/Specification

I can't even find that it says it has Wi-Fi or Bluetooth but I Googled and that's what the AC stands for and apparently it's Intel based... Not a very specific spec sheet in my opinion. Id love to know what exact Wi-Fi card is used.

Update: seems I missed the details tab.... I now see the type of card. But I still want to confirm that it's presented as a PCI device.

  • It clearly states in the datasheet that this board has WiFi and Bluetooth, even specifying the chipset as an Intel Wireless-AC 8265, according to msi.com/pdf/presale_v2/Z370-GAMING-PRO-CARBON-AC and Google confirms that chipset is available for USB or PCIe interface, which one is implemented honestly isn't relevant as both are more than sufficient to handle the potential bandwidth needs. These answers are pretty easy to Google, took me just a few seconds. – acejavelin Apr 11 '18 at 3:40
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    @acejavelin how it's presented to the OS is extremely relevant as I'm looking to do PCI pass-through via IOMMU/VT-d. It is in fact the only reason I asked the question. – FreeSoftwareServers Apr 11 '18 at 3:42
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    Your question hinted more that you couldn't verify if the board had WiFi and Bluetooth, sorry if I misunderstood. I would find it very unusual for a mainboard, especially a gaming one, to use USB as it's WiFi interface... It would use the PCIe interface. – acejavelin Apr 11 '18 at 3:44
  • @acejavelin I've never had a motherboard with onboard Wi-Fi other than laptops. I figured though, but for the money and time i wanted to confirm. Thanks, your comment plus the answer leave me 100% sure its pci based. – FreeSoftwareServers Apr 11 '18 at 3:48
  • @FreeSoftwareServers I updated my answer slightly. The wireless card is definitely an M.2 style adapter, which is then slotted onto a PCIe x1 card. So I'm fairly certain it must use a PCIe interface. However, there is a USB cable that needs to be attached, although for what purpose, I'm not entirely certain. Could be for the Bluetooth? – Michael Frank Apr 11 '18 at 4:05
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The details page you linked has this information on it:

Intel® Dual Band Wireless-AC 8265 card

  • Supports Wi-Fi 802.11 a/b/g/n/ac, dual band (2.4GHz, 5GHz) up to 867 Mbps speed.
  • Supports Dual Mode Bluetooth® 2.1, 2.1+EDR, 3.0, 4.0, BLE, 4.2

Following that, you can find on Intel Ark that this wireless card could be either PCIe or USB.

Finally, looking at the box art:

enter image description here

There's a PCIe card!

However... and this is where the plot thickens... The product manual reveals the following information:

enter image description here

A USB Cable?!

But then further along it also mentions the following:

Intel® Dual Band Wireless-AC 8265 card
* The Wireless card is pre-install in the M2_3 (M.2 Key E) slot.

There's also this diagram:

enter image description here

All in all, it's quite unclear how exactly this wireless card actually connects to the motherboard, so basically... I dunno?

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    OMG I was so focused on the motherboard.... I didn't even look at the PCI card. For some reason I thought it was literally integrated into the board. It's just a separate accessory. I already own a similar accessory. So in essence you saved me $100 investment in a motherboard accessory I don't need. – FreeSoftwareServers Apr 11 '18 at 3:50
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    I've seen motherboards have a mini PCIe slot right on the board, with such a card installed (probably just an OEM thing), but never a purely integrated chip. Even an integrated chip would probably still be PCIe though. Some weird laptops might connect it through USB but not likely these days. – LawrenceC Apr 11 '18 at 3:55
  • Lol... Wow! I totally missed that as well, but that seems to be a pretty clear answer. – acejavelin Apr 11 '18 at 3:55
  • @michaelfrank I'm actually quite familiar, like I said for some reason I thought it was literally part of the motherboard. The USB provides extra power. I believe you can use it without the USB but the Bluetooth will not work. – FreeSoftwareServers Apr 11 '18 at 4:07
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    @michaelfrank this got me thinking that the USB is more than power because when I use PCI pass-through with a similar device only the Wi-Fi shows up. To pass through the Bluetooth it shows up as an available USB device. To get PCI pass-through to work I have to pass through both separately. – FreeSoftwareServers Apr 11 '18 at 4:14
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As Micheal Frank mentioned in his answer, the motherboard in question comes with a Intel® Dual Band Wireless-AC 8265 card, and Intel's ARK website states: "System Interface Type: PCIe, USB".

This means that the card needs both PCIe and USB to work, not either-or. Typically in these kinds of combo Wifi + Bluetooth cards, whether made by Intel, Atheros (now Qualcomm) or Broadcom, whether in MiniPCIe or m.2 form factor, the PCIe lanes connect the WiFi part, and the USB lanes connect the Bluetooth part.

For example, the following is a screenshot taken from Device Manager on a Windows 10 laptop, where menu "View -> Device by connection" is selected:

Device Manager screenshot

Similarly, on a Linux computer, the WiFi card will show up in lspci, and the Bluetooth card will show up in lsusb.

The MiniPCIe and m.2 connection specifications both include PCIe lanes and USB lanes, and for a combo WiFi + Bluetooth card to work properly, both protocols are required. The PCIe adapter provided with the motherboard routes PCIe lanes on the m.2 connector to the PCIe slot, and the USB lanes to the USB connector, where it must be plugged in to the motherboard's internal USB headers using the provided cable. If the cable is not connected, WiFi may work, but Bluetooth will not work. (Certain models of laptops may have either only PCIe lanes or only USB lanes connected on their MiniPCIe / m.2 slots, and if a combo card is plugged in to those slots, only one function will work.)

Since the OP would like to use PCI passthrough to present the wireless card to a virtual machine, both the PCIe device and the USB device must be passed through if WiFi and Bluetooth are both desired in the virtual machine. (Even then it may not work properly, because PCI passthrough is black magic, and many devices don't like it. I have attempted to pass through a simple PCIe WiFi card before, and never got it to work; your mileage may vary.)

  • Good technical answer. +1 – Michael Frank Apr 11 '18 at 8:15
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    This makes me wonder why the heck it was designed this way....if it has a PCIe interface, why not present as a PCIe switch with 2 devices, one being the Wi-Fi card and one being the bluetooth interface? It seems silly to require both interfaces at the same time. – alex.forencich Apr 11 '18 at 15:08
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    @alex.forencich Think about it... which one would you choose if you were to design a card? Wifi via USB is less efficient (more overhead, less electrical power). Bluetooth via PCIe isn't defined in the HCI specs, so you would have to integrate a PCIe USB host controller. – AndreKR Apr 11 '18 at 17:46
  • @twisteroidambassador I to have had trouble passing through a Wi-Fi PCI Nic. I have only been successful with esxi and even then not 100% of the time. I noticed in esxi 6.5 that the USB Bluetooth was no longer present but in esxi 6 it was. I completely was unable to do it via KVM passthrough. – FreeSoftwareServers Apr 11 '18 at 23:25
  • @AndreKR obviously wi-fi would have to be connected via PCIe to get the necessary bandwidth. Interesting to note that USB is the only 'standard' way to provide a bluetooth interface, that I was not aware of. Obviously there must be some advantage to adding the USB interface electronics and drivers instead of implementing a PCIe switch, USB host, and USB device, all on the same die. It's probably just the cheapest solution, after considering die area, testing, driver software, etc. – alex.forencich Apr 12 '18 at 1:21

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