From A4 to today: how Apple became a chip designer
Early iPhones used processors designed by other companies, including Samsung chips based on ARM designs. Apple's decision to build its own began in earnest in 2008, when it acquired the chip design firm P.A. Semi. In 2010 it bought Intrinsity, which added further expertise.
The A4 debuted in the original iPad in 2010 and the iPhone 4 the same year. It was the first system on a chip Apple could call its own, even though it still used ARM building blocks.
Over the next few years Apple grew its chip team and published steady gains. The A7, in the iPhone 5s in 2013, was the first 64-bit processor in a smartphone, which caught rivals off guard.