Microsoft does not own Apple. Apple is an corporation with an independent stock listing on the NASDAQ Global Select Market. In 1997, however, Microsoft purchased roughly $150 million dollars worth of non-voting Apple preferred stock.
In 2001, Microsoft exercised an option to convert the preferred shares into about 18.1 million shares of common stock. These common shares were sold by Microsoft over a two-year period until, by 2003, Microsoft had divested itself of any ownership in Apple. During the 1997 to 2003 investment period, Microsoft and Apple agreed to a broad patent cross-licensing arrangement. Microsoft supported its Microsoft Office software suite for the Mac for five years while Apple made Internet Explorer the default Web browser for its systems.