The iPhone itself is a collection of electronic components such as chips, modules, and so on. The internal teardown images can be found at the following URL: https://www.ifixit.com/Teardown/iPhone+6+Teardown/29213
The following image shows the internals of iPhone 6:
As you can observe in the preceding image that iPhone 6 comes with faster A8 processors with 1 GB of RAM. I would encourage you to explore rest of the hardware components and differences between various iPhone models. Make sure you have knowledge of hardware of target device before start working on it.