If you look at the stocks like C, or S. You'll see once a certain price level is taken out it is a RUSH to fill the new bids or offers, and whoever can get there the fastest has a huge edge, as you are first in line to be filled. Now I have to imagine there are several co-located computers trying to do this. Who gets the top spot? It is one guy all the time? Or do the ecns choose randomly amongst the black boxes trying to send there bids there? How is this determined? Also how much does it cost to get there first?