Switch from Power PC to Intel, and then from Intel to ARM. I'm using Apple as a tipping point, to when the new architecture was so much better than the old it completely took over. Obviously with 90% of Apple devices being ARM already it was an easier choice for them this time. But as each Architecture gets more power as the market is many times bigger, it may be more difficult for the new entrant.
That's why RISC V's win (if it occurs) will be because it's Open Source. Linux won in 30 years against everyone else due to that.
I'm guessing it already has a lot of influence over Arm though and there are other factors that strongly act in favour of staying with Arm.
If Nvidia takes over Arm though and starts making life difficult for the ecosystem then that could change ....
It would be interesting to know how important the ARM instruction set is to Apple.
That, of course, is just with the Mac since Apple previously used variants of the MOS 6502 (1975 and allegedly an illicit clone of the MC6800). Apple, Atari, Acorn, Commodore (the owner of MOS for several years), BBC, Oric, and Nintendo used it in multiple systems each. Apple, Acorn, and Nintendo built additional systems on its updated sibling the WDC65816 series (1983).
The the 6800/6809/Hitachi 6300/68k/Dragonball/Coldfire dynasty and the bastard MOS6502/WDC65816 families were collectively basically the ARM of their day in a way. Everyone targeting low priced or power-sipping was building platforms around them at one time or another. Acorn went from a customer to a major competitor and successor.
It should be noted that the PowerPC and the whole POWER ISA multi-platform family was largely inspired by Apple in the first place. They were talking to IBM about a new platform and invited Motorola to the talks as their long-time processor provider. They formed the "AIM Alliance" that eventually morphed into the POWER Foundation and OpenPOWER initiatives. I can't really speak to how much of POWER ISA is inspired by Motorola's own "RISC" processor, the 88000 series.
