A concern among some traders is the ongoing fragmentation of the stock market. Shares of IBM list on the New York Stock Exchange, but if you buy them, the actual purchase might occur on the NYSE, the Nasdaq, an ECN, or a regional exchange, all of whom might be showing a different price.

However, stock market execution is rather simple compared to the way foreign exchange trades occur. There is no central exchange for spot forex; most trading is done via something called the Interbank system, which consists of institutions around the globe that trade foreign currencies on a regular basis and thus have a large supply on hand - banks, obviously, but also insurance companies and other large firms that do business internationally. For companies in the Interbank, trading forex is necessary as a way to hedge against fluctuations in foreign currency prices, as well as to speculate on currency values.