Application Processor

The application processor is the technical term given to a processor of an iDevice. There have been many incarnations of processors for Apple's mobile devices.

Features
Each revision is an ARM SoC tailored to the device's needs. Up through the S5L8922 for the iPod touch 3G, all revisions were altered versions of existing ARM processors. With the S5L8930 (A4), Apple decided to start to design their own chips with a built in AES and a built in GPU allowing for up to (purportedly) 9x faster graphics.