“The whole purpose of the BootROM and EFI phases is to get to load and run the macOS kernel and its extensions, which is what boot.efi, the ‘OS X booter,’ finally does,” The Electric Light Company writes. “Although boot.efi doesn’t suddenly vanish, from here on it is very little needed.”
“The two important topics with respect to the boot process are IOKit and extensions,” ELC writes. “IOKit is remarkable, possibly unique, as it uses object-oriented principles in classes and overloading. Instead of each driver being entire within itself, it declares itself to be a member of a particular family, so letting a driver re-use all the code which it has inherited from that family class, and it only has to implement the functions which differ.”
ELC writes, “Until High Sierra, Apple controlled extension development with special developer signatures, but macOS 10.13 introduced another level of protection: User Approved Kernel Extension loading.”
Read more in the full article here.
MacDailyNews Take: Combined with copious links to some pretty dense material, here’s pretty much way more than most people want or need to know about the macOS boot process.