Now the clock begins on Apple switching to RISC-V
Rather, RISC-V's primary advantage over ARM is its openness; vendors can do whatever they want with the ISA without having to pay license fees or maintain compatibility. But this doesn't affect Apple at all; they co-founded ARM, and they have a huge amount of influence over the direction of the architecture along with some sort of special license that allows them to do things other CPU vendors aren't allowed to do (https://news.ycombinator.com/item?id=29782840, https://twitter.com/stuntpants/status/1346470705446092811).
Developing an entirely new high-end CPU mircoarchitecture takes many years and many billions of dollars. It's not something Apple's going to do unless they have a very, very good reason -- and RISC-V being really cool is unfortunately not a good enough reason.
The fact that Arm64 doesn’t have compressed instructions is obviously a very deliberate choice, thus I can’t agree with the notion that RISC-V compressed instructions could be a potential “advantage” over Arm64. Their absence is a massive advantage in many ways that I have explained over and over on HN and it’s the single biggest stupidity in RISC-V for high-end perf (not microcontrollers).
ARMv8 is a nice ISA, and the work that architects do is critical, and it's not easy to develop a precise, clean, extensible, and relatively bug free ISA. But there is relatively little real innovation in it. It's a pretty conventional RISC, warmed over for the modern era. In fact no ISA has any real magic, that's all in the silicon.
There's certainly not hundreds of millions of dollars per year worth. That money is only paid because of the proprietary lock-in and ecosystem around the ISA, which is similar to the proprietary software model, so at some point it would be easy to imagine large chunks of the industry deciding to break away and go to something more open.
It may not inevitably displace ARM entirely, and ARM Ltd might change their ways or open their ISA to prevent it. But it could easily happen too, in the next decade or so.
For that it probably gets access to the full range of Arm IP, including for example the IP associated with big.LITTLE - and there are likely to be others.
There are two areas where RISC-V, for example, does have present a clear advantage for firms: where firms want to innovate on top on an ISA (eg Tenstorrent) or who want to shave cents off their BOM (eg WD).
> I suspect Apple pays very small fees which are not material in the context of the Mac.
Why do you suspect they are very small?
I don't see how that follows. You don't know what their royalty arrangement is. It's probably related to the value of the chip sold. If they sell 20 million macs a year and pay ARM 2 bucks a chip that's 40 million every year. If macs have a gross profit of a couple of billion that's not insignificant. Could be 5% of that. Not to mention several hundred million a year for iphones. Lot of money to pay to be locked into a proprietary ISA when you almost entirely support your own ecosystem, compilers, OSes, etc anyway.
Oh and they are clearly not locked in as they have just changed the ISA for Macs anyway.
That's a lot.
> for which it probably gets access to all of Arm’s IP (eg big.LITTLE) as well
That isn't how their licensing works. They license IP and charge royalties for cores. Apple would pay extra to license ARM Ltd cores they use.
I don't know if there are any public details about license and royalty structure for Apple, but this is ARM Ltd's core business and it's how they make their money. So, probably.
> And of course, they could create any ISA extension, if they wanted.
I'm not sure about that. I think licensees are bound by certain requirements to implement the architecture faithfully. Now Apple obviously has a huge sway and could lobby ARM to make changes it wants. But it does not necessarily have final control of that either.
> But currently they seem to be heading more into the direction of creating additional compute units (like the neural processors) rather than adding new instructions to the CPUs.
Apple designs already deviate from ARM64 specifications, like adding custom instructions: https://github.com/AsahiLinux/docs/wiki/HW:Apple-Instruction...
Apple has invested billions to make a full transition to ARM.
I'd think that they would have to spend at least $50 billion or more to redesign all the Apple Silicon from the iPhone to the Mac Pro, rewrite 5 or 6 operating systems, and beg developers to recompile their apps.
It'd be a nightmare.
I think Apple will stay on ARM for at least 20 years...
I speculate this is somewhat less likely now that the NVidia / ARM deal has fallen through but surely Apple wants the option at least.
Apple probably already use RISC-V designs somewhere in their hardware stack. But the ISA will remain ARM for a long long time.
Even Apple Silicon has a ton of stock ARM cores to control various SoC tasks.