What were the big changes? Beside the obvious changes in hardware components like different custom ARM SoC, different modem chip, added fingerprint sensor, etc.

What were the big changes? Beside the obvious changes in hardware components like different custom ARM SoC, different modem chip, added fingerprint sensor, etc. what are the software changes? I guess you use now fuzzing, static code analysis, semi-automatic proofing on some import kernel drivers. You mentioned boot chain... bootloader, RAM FS, etc. The iPhone OS started as a fork of OSX, which is based on NextStep with the interesting mix of BSD Unix with Mach. So from the OS perspective I guess it still largely resembles the same architecture that was laid out decades ago.