What it is the S&P 500 Index?

The S&P 500 is a list of 500 US corporations, ordered by market capitalization. The list is owned and maintained by Standard & Poor's.
All of the companies in the list are large publicly-held companies which trade on major US stock exchanges such as the New York Stock Exchange and Nasdaq. The market-value weighted performance of the stocks of these companies is known as the S&P 500 500 index. After the Dow Jones Industrial Average, the S&P 500 is the most widely-watched index of large-cap US stocks and is considered to be a bellwether for the US economy. It is often quoted using the symbol GSPC or SPX.
Although the 500 companies in the list are among the largest in the US, it is not simply a list of the 500 biggest companies. The companies are carefully selected to ensure that they are representative of various industries in the US economy. In addition, companies which are privately held and stocks which do not have sufficient liquidity are not in the index. By contrast, the Fortune 500 attempts to list the 500 largest public companies in the United States by gross revenue, regardless of liquidity and without adjustment for industry representation.

How to get real-Time S&P 500 Index data?

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