In a business world so turbulent it feels like one long spin on the Humunga Cowabunga at the water park, an important fact has remained virtually unchanged for decades: who's biggest. Not which company is this quarter's most valuable or most profitable, but who's biggest, the one with more good-old-fashioned sales than any other. Nice to know some things never change, isn't it? Well, it's all about to change.
The most famous thing we do at FORTUNE is publish the definitive list of America's largest companies, the FORTUNE 500. And since the directory's beginning in 1955, the No. 1 company has...