This basically means that even though the slot is PCIe 3.0 x16 (16 lanes) it is limited to x4 lanes from the cpu (Skylake has x24 lanes from the cpu which will be used by the PCIe slots). This is due to the design of the motherboard. A modern gpu uses x16 pcie lanes in a single gpu config (that is 16GB/s of bandwidth between cpu and gpu). In a SLI/Crossfire configuration gpu's use x8 lanes (some xfire config's could use x4). 8gb/s is more than enough for any modern single gpu. However on a mobo with just one x16 PCIe slot, SLI or Crossfire would not be possible at all due to PCIe lanes limitations. However you could use devices such as PCIe ssd's (up to x4 lanes needed ) or wifi cards (x1 lane) etc. in the x4 lanes slot. Better, more...