ATX & PCIe CEM are official!

x16 PCIE slot at bottom for Micro atx mobo : rbuildapc atx slot Processor location Recommended Right of expansion slots, front of back panel IO connectors 1 Expansion Slots The ATX form factor supports up to seven buffalo toro slot demo Form factor of ATX expansion slots The closest I can find it the specification on form , here

slot lgo The IO to PCIE spacing for slot '1' is standard between motherboard sizes as I understand it The rest then follow 'down' the board