Market cap is the dollar value of a company's outstanding shares. On Wednesday, Apple Inc.'s shares slipped $1.11 to close at $244.11, making its market cap about $222 billion.
But Microsoft Corp.'s stock fell $1.06, or 4.1 percent, to close at $25.01, for market cap of about $219 billion.
The only U.S. business with a higher market value is Exxon Mobil Corp. The oil company's market cap is about $279 billion, based on Wednesday's closing price of $59.31.