According to MarketWatch, Apple has surpassed Microsoft’s market capitalization on Standard & Poor’s S&P 500 index, a move that makes Apple the second-largest company on that index behind only to energy giant Exxon Mobil—or so claims “Apple’s market capitalization as calculated by S&P rose today to $241.5 billion, thus topping Microsoft’s, which stood at $239.5 billion. The “market cap,” as this key financial metric is often called, represents the total value of all outstanding shares of a company—in other words, number of shares times their price. That makes market capitalization an indicator of how much the markets think that a particular company is worth, rather than an objective measurement of a company's assets and liabilities. S&P 500 index, in particular, is based on a company's “float-adjusted” market cap—that’s the value of all shares that’re available on market for sale at any given point in time. While that’s of particular interest to investors—who, after all, are looking to actively trade in a stock—this number doesn’t include shares that’re held by investors who’re not interested in trading. And that makes a big difference: when all shares of both companies are taken into consideration, Microsoft’s full market cap still outstrips Apple's by $275 billion to $241 billion,” said MarketWatch.