[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.

[zepto]

I haven’t seen their license but they founded ARM and even though they don’t retain any ownership of the business I have heard that they retain a license that allows them to do pretty much whatever they like with the architecture in their own products.

[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).