Not a surprise here, the Apple iPhone 4S comes with the same system on chip as the iPad 2 tablet, Apple's own A5 model.
Apple would only say that it is a dual core model which performs twice as fast for CPU tasks and comes with dual core graphics which provides up to seven times the graphics performance of the previous generation.
We suspect that the SoC on the iPhone 4S is likely to have a different clock speed compared to its iPad 2 counterpart, probably clocked higher because of the real time strain placed on the system by a resource-hungry service like Siri. The A5 in the iPad 2 is clocked at 1GHz and it is worth noting that the A5 is not even mentioned on the spec page.
Given that the A5 was probably fabbed around at the same time as the Nvidia Tegra 2, Apple is likely to have a product that will be superseded over the next few weeks by the new quad core Tegra 3 SoC.
The latter us is more than likely to go into smartphones by the beginning of next year and trounce the iPhone 4S in most cross platform benchmarks.
At the same clock frequency, the Cortex A9-based A5 is likely to be 25 per cent faster than the Cortex A8-based A4. Add in twice the amount of cores and it looks likely that Apple has deliberately quoted very conservative performance figures.