Trade Cabot Microelectronics
S&P 500 stock market index, held by The S&P Dow Jones Indices, includes 505 common shares issued by 500 large-cap companies traded on U.S. exchanges (including the 30 companies that make up the Dow Jones Industrial Average), covering about 80 percent of the U.S. stock market through capitalization. The index is likely through free market value to float, so the most valuable companies represent relatively more than the index. Index components and component weights are regularly updated using the rules published by the S&P Dow Jones indices. Although it is called the S&P 500, the index contains 505 shares because it includes two categories of shares of 5 of its constituent companies. S&P Dow Jones index updates components of the S&P 500 index periodically, usually in response to acquisitions, or to keep the index up-to-date with the growth or shrinking value of different companies. Between January 1, 1963 and December 31, 2014, 1,186 index components were replaced by other components.