Apple has been listed as the second-largest company on the S&P 500 Index, on the basis of market capitalization, topping its biggest rival Microsoft, on Thursday. This has been observed in the wake of the favorable investor reactions to Apple Inc.

As per the data provided by Standard & Poor's index services unit, Apple has managed to reach the level of $241.5 billion in market capitalization, outdoing Microsoft's $239.5 billion value in the capitalization.

The S&P 500 is essentially float-adjusted just like other Standard & Poor indexes. For estimating the index's compositions, S&P basically keeps out those shares which are not provided to public investors.

According to FactSet Research, around 87.7% of Microsoft shares are publicly-floated in contrast with the 99.2% of Apple's.

Overall, S&P admits that Microsoft's market capitalization is still greater than that of Apple.

Bill Koefoed, General Manager for Microsoft investor relations said that if Bill Gates and Steve Ballmer don't trade their shares, this doesn't necessarily mean that they are excluded from market cap.

"Apple is bigger on a float basis, which is what the index is", said S&P's Senior Index Analyst, Howard Silverblatt.