Possible values of an option:
[Auto], [x2 Mode (compatible)], [x4 Mode (fast)]
The option description:
The option limits quantity of used lines PCI Express for the second слота PCI Express 16x. Value installation [Auto] will be the best variant, allowing to involve greatest possible in the given configuration quantity of lines. But at desire you can independently limit quantity of used lines PCI Express to 4 (value [x4 Mode (fast)]) or 2 ([x2 Mode (compatible)]).
On a part motherboards, owing to restrictions of the applied chipset, the second слот PCI Express 16x in a reality has not 16 lines PCI Express that like would follow from its name, and 8, 4, 2 or, sometimes, only 1 line. Application of universal socket PCI Express 16x allows to establish in the second слот as video cards (to the majority of them, basically, enough 8 or 4 lines PCI Express for normal work even in mode SLI or CrossFire), and high-speed cards of expansion PCI Express 8x or PCI Express 4x, and also the usual cards of expansion using only 1 line PCI Express. So be not surprised to so strange set of values for this option.
For the chipsets having only 20 lines PCI Express, use by the second слотом PCI Express 16x 4 lines leads to that usual слот PCI Express is disconnected — for it simply does not remain free lines (remained 16 are involved by the first слотом PCI Express 16x).
Other options identical to destination: