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What happens during startup?
Explains the sequence of events from Boot ROM to FileVault login, what storage is accessible at different times, and where the code is.
Boot ROM, which ends in DFU mode if there’s a problem, otherwise it hands on to the Low-Level Bootloader (LLB) and iBoot (Stage 2), the firmware, that should end in validating and running the kernel, which initially runs on a single CPU core before starting others up and launching launchd, and later unlocking and accessing the Data volume, and progressing to userspace. That means all the code run so far, and almost all the data, are immutable, locked in the firmware or the Signed System Volume (SSV). Posted in Macs, Technology and tagged Apple silicon, BootROM, FileVault, firmware, iBoot, kernel, log.
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