[kbenson]

ARM based processors which are used in most mobile devices and use a different instruction set, as opposed to x86 based processors, such as those available from Intel and AMD. Apple licensed the ARM technology and builds their own chips using it, and really good chips at that. So good, that some people are now calling for Apple to release an ARM based laptop (which has been done by others, but not to much popularity).

There would be advantages (power savings) and disadvantages (most existing MacOS software wouldn't work until recompiled at a minimum)

[beat]

Odds are they already have ARM-based Macs in house, with all the cross-compilation stuff worked out. The reason they haven't made the switch yet isn't because of work they haven't done.

Back when they switched from the PowerPC chips to x86, it was revealed that they had been building experimental x86 Macs in-house for years. That's just good planning.

[kbenson]

Oh, I'm fairly sure they've tested all their MacOS core software that comes with the OS (and the OS), but all the third party stuff and things in the MacOS app store likely need a lot more time. (at least for those that weren't already shipping iPhone/iPad versions).

[duskwuff]

My expectation is that any ARM laptop/desktop made by Apple would include some form of x86 emulation, just like they used during their PPC-x86 and 68k-PPC transitions.