Well x86 at one point, arm both the 32 and 64 bit versions. I think they had RISCV support in their source tree at one point but not really at a commercial level. It does cover a lot different levels of hardware though
Does Apple use macOS in servers in its datacentres? Or are they all Linux?
Surely at a minimum they need macOS for CI.
Apple does have one advantage here-they can legally grant themselves permission to run macOS internally on non-Apple hardware, and I don’t believe doing so legally obliges them to extend the same allowance to their customers.
But that might give them a reason to keep x86_64 alive for internal use, since that platform (still) gives you more options for server-class hardware than ARM does
They do run Apple Silicon in data centers, so perhaps another custom version of Darwin + their system frameworks. It is hard to tell without some leaks :)
For Private Cloud Compute: “a new operating system: a hardened subset of the foundations of iOS and macOS tailored to support Large Language Model (LLM) inference workloads while presenting an extremely narrow attack surface.” https://security.apple.com/blog/private-cloud-compute/
Well there were still the historical arm32 chips in their iOS devices, but until recently the watches were a cursed arm64_32 (or something like that) which is arm64 with 32 bit pointers iirc.
I should have just soureced this, They had PowerPC not RISCV in there source tree that was the X factor one. The Arm32 bit variant is closed sourced (leaked before) but was supported until IOS 11. XNU is really old almost 30 years! And before XNU there was the MACH kernel and the larger BSD tree it was built on which is an argument that it probably had a initial MIPs release too but I couldn't source the truth on that.
I'm sure there's vestiges of them somewhere, but the underlying support (the architecture specific parts of the mach portion of the kernel) is gone for those archs.
I wouldn't be surprised if they keep a minimal Power base maintained behind closed doors. It's how they managed to jump ship to intel so quickly, they never stopped maintaining NeXTSTEPs x86 port
Apple's ARM implementation is in a really good place right now. It would take something extremely compelling to get them to consider any other architecture for an application processor, especially considering that it'd mean giving up some degree of control.
Power is probably not where Apple would choose to go unless something really unusual happened. It's essentially just IBM's pet architecture at this point.
When I mean minimal arm base, I basically mean making sure XNU at least compiles on PPC64. I don't doubt they'd likely never have a use for it, but they maintained intel support behind closed doors when macos forked from NeXTstep and nobody thought they'd need that
They've been making quite a few changes to the virtual memory code over the past decade, and keeping those vestigial arch's around is a pretty big maintenance burden. It'd probably be less work to just add the arch as if it were new when it's needed at this point since the kernel itself is pretty portable.
