The ones I've seen so far have either four or five slots. The lane allocation isn't set in stone; I've seen a few that have 3-x16, 1-x1, and 3-x4 (M2) [1] but I

The ones I've seen so far have either four or five slots. The lane allocation isn't set in stone; I've seen a few that have 3-x16, 1-x1, and 3-x4 (M2) [1] but I've also seen one that has 4-x16, 1-x1, and 2-x4 (M2) [2]. I assume those motherboards are using PCIe switches, but there are plenty of configurations that wouldn't require the switch. [1] https://www.pcper.com/news/Motherboards/Computex-2017-ASRock-Shows-Two-X399-Threadripper-Motherboards https://www.pcper.com/news/Motherboards/Computex-2017-ASRock... [2] http://wccftech.com/gigabyte-x399-aorus-gaming-7-amd-ryzen-threadripper-motherboard-pictured/ http://wccftech.com/gigabyte-x399-aorus-gaming-7-amd-ryzen-t...