So far we have not seen many native U.2 (SFF-8639) connectors for SSD drives on consumer motherboards but we are hopeful somebody will put 2 of them on a motherboard so that extreme SSD drives like the Intel 750 in 2½” 15mm form factor can be installed. The Intel 750 is also available as a PCI Express card which can be installed in a UEFI machine with NVMe support as a boot device.
U.2 uses four PCI Express 3.0 lanes to provide extreme bandwidth to support SSD drives and the newer Intel Optane phase change drives which are even faster.
We have seen PCI Express x16 cards with four U.2 connectors but they are over $1,000 each which is out of the reach of mainstream consumers.
SATA ports are fine for hard disks but SSD drives are were the bandwidth of PCI Express is needed the most. U.2 has double the bandwidth of M.2 which is what is needed to get over 4GB/s in speed.
M.2 was designed to replace the mini PCI Express slots for laptop and mobile machines but desktop machines have also adopted the technology for motherboard mounted SSD drives.
Using a SSD with U.2 can boot Windows is < 10 seconds with Steam in the autorun on a modern machine with 32GB or more memory.
There are low cost adapters to connect U.2 to a M.2 slot which has half the PCI Express lanes. This tends to throttle the SSD somewhat. This is due to the SSD being designed for using four lanes while M.2 is only two lanes. Adapters range from $15 and up.
Intel has also indicated they will ship their 750 drives with the adapter included so that they can be installed in consumer machines more easily. M.2 slots are now increasingly common on recent motherboards. M.2 only uses 2 lanes while U.2 uses 4 lanes which puts more demand for a higher end processors with enough PCI Express lanes.
GIGABYTE AORUS Z270 KILLER DOUBLESHOT X3
The Gigabyte Aorus Killer Doubleshot X3 is the first motherboard seen while searching for a consumer motherboard with the higher bandwidth SSD capability, Gigabyte offers three U.2 ports to handle a RAID setup using the Intel 750 SSD drives.
ASUS PRIME X299
The Asus Prime X299 has a single U.2 that is disabled by default as it shares lanes with the second M.2 slot.