[Someone]

> Apple has a fairly long history of keeping cross-platform ports alive even if they aren't publicly available (that's why the transitions from 68K->PowerPC->Intel->Apple Silicon have been relatively smooth)

I don’t fully follow that logic. There never was a cross-platform Mac OS until PowerPC. The 68k to PowerPC transition had the first PowerPC version running most of the OS in emulation, and an incredible hack (in the good sense) to allow 68k code call PowerPC code and vice versa for all the different calling conventions that the 68k version of the OS used.

I think the later transitions only worked because they had moved to the Unix-based Mac OS X before that, ditching lots of assembly code. It’s Unix that’s portable.

For both PowerPC to Intel and Intel to Apple Silicon I guess it also helped that they already had code for lots of time-critical parts of the OS. For the first, they had Intel code in QuickTime for Windows, for the second, ARM code in iOS.