NYSE:
10.03 x 500
10.04 x 100
Market order at NYSE for 500. All your order will be filled at NASDAQ. Correct?
By the way are the different ECNs and other exchanges linked to NYSE?!
Nope, only the top 100 shares will be executed on NASDAQ.
Yes, exchanges route orders to each other not because they want to give away their market share, but because they're required to do so by requlators. So they all behave very similarly.