what is the term which differentiate the Apple A7 and Apple A8 system on a chips?
Apple A8 The Apple A8 is a 64-bit ARM-based system on a chip (SoC) designed by Apple Inc. It first appeared in the iPhone 6 and iPhone 6 Plus, which were introduced on September 9, 2014. Apple states that it has 25% more CPU performance and 50% more graphics performance while drawing only 50% of the power of its predecessor, the Apple A7.
PowerPC G4 PowerPC G4 is a designation used by Apple Computer and Eyetech to describe a "fourth generation" of 32-bit PowerPC microprocessors. Apple has applied this name to various (though closely related) processor models from Freescale, a former part of Motorola. Motorola and Freescale's proper name of this family of processors is PowerPC 74xx.