The Standard & Poor's 500 Index includes: all of the stock listed on the New York Stock Exchange. 30 of the largest (market capitalization) and most active companies in the U.S. economy. 500 firms that are the largest in their respective economic sectors. 500 firms that are the largest as ranked by Fortune Magazine.
The advantage of the limit order is that the investor makes the trade at the desired price. The disadvantage of the limit order is that the trade might not be executed at all. They can be used only to buy stock.