While reading about PCIe and PCI I came across webpages detailing about the difference between Serial and Parallel communication. What I found out was one particular statement i.e.
Some things like PCI Express do the best of both worlds, they do a parallel set of serial connections (the 16x port on your motherboard has 16 serial connections). By doing that each line does not need to be in perfect sync with the other lines, just as long as the controller at the other end can reorder the "packets" of data as they come in using the correct order. Source
What i think is reordering will come into picture even in parallel communication also. So how will 16 parallel set of serial connections avoid the problem of synchronizing the data?