but as joseph mecane of n.y.s.e. euronext explains, many retail brokers use these systems to provide rapid order execution with very low commission charges. >> a lot of retail and little investor trade activity, whether they realize it or not, actually comes through servers that are co-located. so i think, you know, it is something that is available to a big part of the market, whether people realize it or not. >> reporter: during the flash crash on may 6, tradeworx, like many other high frequency firms, stopped trading when price swings appeared irrational to the humans monitoring the computers. >> the only responsible thing to do when clearly erroneous prices are being transacted is to stop trading. and instead of breaking trades after fact, which is a terrible practice, what the exchanges should be doing is preventing those trades from ever taking place in the first place, and that is what these circuit breakers would do. >> reporter: narang says he fully supports the circuit breakers so that the machines can take