Original: The chip commercially debuted with the release of Apple's iPad tablet; followed shortly by the iPhone 4 smartphone, the 4th generation iPod Touch and the 2nd generation Apple TV. It was superseded in the second-generation iPad, released the following year, by the Apple A5 processor.
Simplified: The Apple A4 is a microprocessor designed by Apple and manufactured by Samsung and first used in the iPad tablet computer, then in the iPhone 4 smartphone.