What kind of improvements the A5 CPU in the Apple iPad 2 has over the A4 have yet to be revealed and it is likely that only a thorough analysis by a company like Chipworks of the die itself will determine that after launch.
For now, there are only speculations, however wild they are. We know that Apple has doubled both the amount of GPU and the amount of CPU on the A5 while keeping the speed constant and promising double the performance.
Could it therefore be that the A5 kept the slightly enhanced Cortex-A8 base but doubled the amount of core and moved to a much thinner manufacturing process?
Such a move would decrease the amount of power consumed compared to the previous generation; the current A8 is manufactured by Samsung on 45nm and one can expect the A5 to be based on a 32nm manufacturing process.
The 9x faster graphics though would mean moving to a different GPU family altogether, one which probably consumes much more power compared to the previous generation.
In effect, doubling of the number of GPU cores and the move to a new generation is what might have convinced Apple to stick to the Cortex A8 rather than move to the A9 as the power consumption for the GPU and CPU even out.
Yet we are still at a loss to explain how Apple has manage to deliver what appears to be same battery (Built-in 25-watt-hour rechargeable lithium-polymer battery) with exactly the same metrics, keeping the same screen but with a 33 per cent thinner enclosure.