Hello. I understand that my questions are so naÃ¯ve, but I want to thank everyone for reading and replying to my post. I want to trade highly liquid US equities at Nasdaq, NYSE and Amex. I used to think that four-letter stocks such as AAPL or BIIB are traded at Nasdaq and three letter stocks such as IBM or CNX are traded at NYSE only. However, I learn that US stock markets are evolving. Now stocks such as AAPL or IBM may be traded at NYSE, Nasdaq or AMEX or any other regional exchanges, or ECNs. Is this true? Where can I get more info on this? In addition, what is exactly an ECN? I learn that big ECN names such as ARCA, EDGX or BATS. How are they different from a market maker? How are they different? I was told ARCA can trade only 100K shares minimum for a particular stock. Is this true? If it is the case, I guess retail traders such as me will never be able to trade at ARCA. Thank you again for reading and reply!