How Apple overtook Google, Walmart, Microsoft and Exxon

The closing bell rang Wednesday with Apple's market cap, for the first time, at No. 1 

Chart courtesy of ycharts.com

Apple (AAPL), for now at least, is the world's most valued company by market capitalization (determined by multiplying a company's stock price times number of shares outstanding). Here's how it happened:

• It caught up to Google (GOOG) in mid-2009
• It overtook Walmart (WMT) in March 2010
• It passed Microsoft (MSFT) in May 2010
• It caught up to Exxon Mobile (XOM) Tuesday and closed higher, for the first time, on Wednesday, Aug. 10, 2011