With Apple's acquisition of PA Semiconductor, it's been designing and churning out its own CPUs, including the 1GHz A5 processor in the iPhone 4S and the A5+ processor in the third-generation iPad.
Many people thought we'd get the A6 processor with the new iPad -- and that it would be a quad-core chip. But we didn't (the A5+ is dual-core chip). The A6 chip is reportedly a 28-nanometer process, as compared with the A5's 45nm, meaning lower energy consumption and higher speeds.
The faster processor would improve the performance of Siri, the iPhone 4S' integrated voice assistant, as well as a host of other features, such as still and video image capture.