If there are 2 slots, I'm assuming that one is either PCIe x8/16, and the other is PCIe x1. The difference between the two is lane width, the amount of pins and the maximum data transfer rate. Consider the following:
PCI Express 1x - 250 [500] MB/s
PCI Express 2x - 500 [1000] MB/s
PCI Express 4x - 1000 [2000] MB/s
PCI Express 8x - 2000 [4000] MB/s
PCI Express 16x - 4000 [8000] MB/s
The first number represents data speeds in one direction, with the figure inside the braces being the combined data rate of both directions. Usually the way slots are configured, the first slot will have a higher data rate, with the second being slower. So, in your case, you've probably got 1 PCIe x8/16 and 1 PCIe x1.
Not really sure what else you want to know, but I hope this helps...