Rival electronic exchange operator BATS has already filed an S-1 with the SEC. Both firms have come a long way from the days when they were breaking ground as so-called ECNs. As formal exchanges, it has not always been a smooth ride. Recall that in October, the SEC sanctioned Direct Edge for weak internal controls over its systems, which resulted in millions of dollars in trading losses and a systems outage. One incident involved in untested computer code changes, which caused the two exchanges to overfill orders submitted by three members. The second incident occurred when an EDGX database administrator inadvertently disabled a database, disrupting the exchange's ability to process incoming orders, modifications, and cancelations. http://www.fiercefinanceit.com/story/direct-edge-mulls-ipo/2012-03-01