 The iOS kernel is the XNU kernel of Darwin.The original iPhone OS (1.0) up to iPhone OS 3.1.3 used Darwin 9.0.0d1.iOS 4 was based on Darwin 10. iOS 5 was based on Darwin 11. iOS 6 was based on Darwin 13. iOS 7 and iOS 8 are based on Darwin 14. iOS 9 is based on Darwin 15. iOS 10 is based on Darwin 16. iOS 11 is based on Darwin 17. iOS 12 is based on Darwin 18. iOS 13 is based on Darwin 19.

iOS utilizes many security features in both hardware and software.