А вообще, в современных железках эппл есть применение и современным микроядрам. Например тот-же Secury Enclave Processor пашет под L4 microkernel:

«The Secure Enclave Processor runs a Secure Enclave OS based on an Apple-customized version of the L4 microkernel. This Secure Enclave OS is signed by Apple, verified by the Secure Enclave Boot ROM, and updated through a personalized software update process. An example of some built-in services that utilize the hardware protected Secure Key Store:
Unlock of device or account (Password & Biometric)
Hardware Encryption / Data Protection / FileVault (Data-at-Rest)
Secure Boot (Firmware and OS Trust and Integrity)  
Hardware control of camera (FaceTime)»