Apple's iPhone business, which didn't exist three years ago, now represents a whopping 40% of the company's revenue, and has been the company's biggest revenue generator for three quarters in a row.

During the March quarter, iPhone revenue grew 124% year-over-year to $5.4 billion, or 40% of Apple's $13.5 billion in total revenue. Because of high profit margins on the iPhone, it's likely Apple's biggest profit contributor, too. (But that's another chart.)

Apple's second-biggest business is its Mac computer division, which grew 27% year-over-year in the March quarter to $3.8 billion, or 28% of Apple's overall sales.

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