The S&P 500 and How It Works

How the S&P 500 Is Different from Other Stock Market Indices

The S&P 500 has more large-cap stocks than the Dow Jones Industrial Average. The Dow tracks the share price of 30 companies that best represent their industries. Its market capitalization accounts for almost one-quarter of the U.S. stock market.
The Dow is the most quoted market indicator in the world.
The S&P 500 has fewer technology-related stocks than the NASDAQ. The NASDAQ also includes the stocks of companies that are privately-owned. 
Despite these differences, all these stock indices tend to move together. If you focus on one, you will understand how well the stock market is doing. In other words, you don't have to follow all three.

Milestones

Date	Close	Event
January 3, 1950	16.66	Record closing low. 1st close.
June 4, 1968	100.38	1st time above 100
October 19, 1987	224.84	Black Monday largest % loss (20.5%)
March 24, 1995	500.97	1st close above 500