[mavhc]

They sold their 40% stake in ARM when they were short of cash.

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.

[klelatti]

On the Apple specific case I think any move to RISC V would be because it would want more control than it has with Arm. It could then take the RISC V ISA in the direction it wants.

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 ....

[mrweasel]

Apple is really interesting, with chip design being moved inhouse and the ease of which they seem to switch architecture they could move away from ARM if the Nvidia purchase happens. I think they’d want to avoid it, at least for the next 10 years.

It would be interesting to know how important the ARM instruction set is to Apple.

[klelatti]

I wouldn't be completely surprised if there is a box running a build of Mac OS for RISC V somewhere in Cupertino!

Seriously though, I suspect that the ISA isn't that important for Apple but on the other hand I think they're probably quite happy with the direction of the Arm ISA (probably had a big say in parts of it) and it would take quite a lot to push them away.

I think that the odds on the Nvidia takeover are quite small by now so don't think a move likely at all.

[mavhc]

Apple's aggressive removal of legacy stuff means the apps they do have are mostly kept up to date, so they have that going for them. On the desktop the major Mac OS only apps are now a) owned by Apple and b) rewritten from scratch so are easy to port to ARM, and therefore most likely, anything else.

Will RISC V do what ARM did to x86? Start at the low end, be more open, and slowly take over.

[klelatti]

I think that's unlikely - Arm gradually replaced a number of in-house ISA's and designs because the economics didn't support each firm doing their own thing. I'd be surprised if in many cases - except for eg Western Digital - the economics of going RISC-V make sense.

[kube-system]

Given Apple's history, and their business style, I don't think they have loyalty to any architecture or any specific technology in particular. They're care about product first, and choose whatever technology they need to choose to get there. https://youtu.be/oeqPrUmVz-o?t=113

[klelatti]

It's a great clip - possibly my favourite Jobs clip.

Agree with the point 100% but Apple also has a history of long and sustained investments in key parts of the stack where it sees long term value - including compilers and silicon - and long relationships with suppliers. I suspect their relationship with Arm is in that category and so in the absence of something that is demonstrably better, then that will continue.

[zepto]

> they could move away from ARM if the Nvidia purchase happens.

The Nvidia purchase is irrelevant to Apple. They have a license that won’t be impacted.

The only thing that would make them move away would be a performance bottleneck in the architecture that necessitates a shift.

[klelatti]

> Still leaves Apple open to potential Nvidia's changes to the ISA's direction (and the ISA won't stand still). I assume a full fork of the ISA isn't on the cards even for Apple.

[zepto]

> I assume a full fork of the ISA isn't on the cards even for Apple.

Why do you assume this?

[klelatti]

If you've seen their license then happy to be corrected but typically an architecture license wouldn't permit them to do precisely what they want with the ISA with no restrictions whatsoever.

[classichasclass]

Pretty sure Apple has a permanent ARM license. They'll watch what happens with Nvidia, but it doesn't really affect them because, as you say, all the secret sauce is in-house.

[klelatti]

Does that give them control over the direction of the ISA - suspect not. Don't think it's really the case then that they're unaffected by the Nvidia takeover.

[lizknope]

Most companies buy the ARM CPU RTL or an existing hardened core for their chip.

Large companies like Apple have an architectural license and implement the entire instruction set on their own.

I worked for a couple of companies with ARM architectural licenses and there was a large ARM compliance suite of tests that had to be run and pass before you could claim that you made an ARM instruction set compatible CPU.

I have heard that Apple does not claim ARM compatibility and doesn't run the compliance suite which allows them a few shortcuts and other optimizations. Apple only cares about running Mac OS and iOS on their hardware so if they were incompatible with Linux/ARM or Windows/ARM they wouldn't really care.

I haven't been able to verify this. Linux/ARM seems to be running okay so far on the new Apple M1 chips.

I don't know if Apple would be affected much if Nvidia buys ARM. Their architecture license to implement from scracth is probably forever but maybe not

[klelatti]

Interesting - especially that Apple gets some latitude on compliance.

Still leaves Apple open to potential Nvidia's changes to the ISA's direction (and the ISA won't stand still). I assume a full fork of the ISA isn't on the cards even for Apple.

[cestith]

I suspect Apple's rights might be spelled out more in the sales contract to SoftBank than in a separate license agreement. Acorn created the ARM processor, but Apple is a cofounder of ARM Holdings (Acorn, Apple, and VLSI Technogology).

[cestith]

Apple switched from Motorola 68k to PowerPC, too, and Sun switched from 68k to SPARC. The Amiga, NeXT, early Palm devices, and the ST were also using members of the 68k family. That's an ISA born in 1979 and largely replacing (and inspired by) the 6800 (1974) which had a 16-bit address bus and 8-bit memory bus and its (binary incompatible but with the same assembly language) little brother the 6809 (1978). The Tandy Color Computer and the Dragon were notable 6809 systems.

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.