> Apple has had access to all Arm’s IP - eg for example on big.LITTLE. Isn’t it right that Apple (market cap around $3tn) actually pays for that IP if they want to use it on another ISA?

Yes, this is my point: there’s little reason to change if you’d just have to keep paying the same.

> Also maybe Apple has decided that Aarch64 is a better choice…

Remember that Apple has a full architecture license and their microarchitecture is their own. Their parts don’t really look like anybody else’s except having mostly the same instruction set. I really don’t think the ISA itself would be anything they would spend any time thinking about either way — other factors dominate.

We're broadly in agreement - my concern was the implication that Apple can't switch because they'd be sued and therefore there is a wider concern for the broader RISC-V ecosystem.

Apple would deserve to be sued if they tried to take Arm's IP that they've had access to for years and apply it to another ISA for free. Doesn't have any read across for a RISC-V designer that doesn't have access to / isn't using that IP.

There are two questions here, not to be conflated:

1: given that apple has their own architecture that happens to implement some of the ARM ISAs, what are they really paying for with their license? The conjecture is: primarily patents. ARM supplies a lot of tooling but I doubt much of that is usable in Apple’s environment, except some of the most surface stuff (ISA conformance, perhaps). At this point I doubt there’s a lot of ARM IP in apple’s parts except for the copyrights on the ISA and patents, which anyone can read.

2: patents can apply to other MPU vendors/developers even if they don’t read them. In fact the “best” (i.e. most horrible) way to enforce them is to wait until vendor gets enough traction and then demand a license be purchased.

1. Maybe, although we don't really know and there is almost certainly stuff that Apple has access to which isn't patents - can they pick up the phone to someone at Arm to discuss and get help on an issue - very likely. Plus as I've said before those patents and associated IP might be integral to Apple's designs and they absolutely should pay for them.

2. Of course, that's just how patents work. But there is no evidence that Arm is doing this.

Overall, I don't agree with the sense that Arm is an overhead for Apple that if it weren't for those pesky patents they would cast aside and cut their costs. I think it's more complex than.