In Pictures: Apple’s most important iPhone upgrade...
The A4 chip, initially introduced with the iPhone 4, is notable because it marked Apple's foray into chip design. No longer content to rely on third parties, Apple's own chip designs are positioned to be more efficient insofar as they can be streamlined for iOS. Since the debut of the A4, Apple has continuously built upon it, most recently with the blazing fast 64-bit A7 processor Apple unveiled with the iPhone 5s last fall.
In Pictures: Apple’s most important iPhone upgrades over the years