I'm digging through history to find an article about Apple's LLVM patches to add a custom instruction only present on A series chip. Due to Sillion announcement it's kinda hard to find - but they did add at least one instruction to ARM instruction set.

From this, and from the very very strong marketing push to NOT use the name "ARM" from Apple, I have a suspicion that Apple Sillicon instruction set won't be a fully standard ARM holdings instruction set

"Apple Silicon" is simply a marketing term for, well, Apple's silicon. They're making this major change to their computers with the promise of better performance, functionality and battery life. Apple's made major investments to have the best chips in their class. Many of the functional improvements come from SoC siblings like GPU, neural cores, hardware codecs, etc. Why would Apple want to give ARM all the credit for that?

Apple isn't shy about communicating to developers that Apple Silicon uses ARM ISA. This is about conveying to consumers their unique platform advantage.

Thanks - I guess I would draw a big distinction between adding a new instruction as part of being first to a new version of ARMv8 - which then becomes part of the standard ISA, and adding a permanently Apple only instruction. Would be very disappointed if it's the latter.

Agreed that the Apple Silicon branding was very strong but assumed that it was just to distinguish themselves with consumers from those who will also use ARM on the desktop.

ARMv8.6 exists

Apple uses V8.4

Current ARM designs use v8.2

As you might suspect, that leaves Apple stuck doing the software support. It also gives them additional instructions that aren't proprietary to them, but are currently unique to them.

> and from the very very strong marketing push to NOT use the name "ARM" from Apple,

This is puzzling to me. I assume it's simple egotism. Apple marketing and also the user community at large tends to present their technologies as exclusive and product categories as invented by them, even when it's a stretch. This has a long history.

There are the AMX machine learning on-die accelerators. I assume there's some new instructions to talk to those.

You don't need special instructions to talk to peripheral devices. The ISA supports that from the get go. As a licensee, you can't add instructions to the ISA, only ARM can do that. That's what they do, they're the custodians of the ARM architecture.

They are probably just peripherals, like the GPU. I'd be very surprised if Apple strayed from the ARMv8 specification and added new instructions for those accelerators.

See this post: https://www.realworldtech.com/forum/?threadid=187087&curpost...

That whole thread is just speculation, same as what we are doing here.

See this post: https://www.realworldtech.com/forum/?threadid=187087&curpost...

As long as it's a compatible superset of ARM64, I don't see a big problem.

Just because you don't see the problem, it doesn't mean it's not there. However you want to put it, you can't add (or remove) instructions at your leisure if you want to keep your license. It does not happen. I can get into details if you want, but I think it's besides the point.

I can see a significant problem with adding proprietary instructions. Would be interested in more detail on ARM specifics if available. Thanks.

1) ARM sells "ecosystem". They can license their IP because licensees know that, once they buy into it, they benefit from a unified ecosystem. Developing and, more than anything else maintaining an ecosystem, is extremely expensive, messy, and error prone. ARM adds value by keeping that ecosystem in order.

2) ARM instructions have a fixed length of 4 bytes. This means that there's a limited number of instructions you can add. Intel, for instance, is different: they have a very complex encoding scheme that gives them, potentially, limitless encoding space.

3) If any licensee, specially a popular one like Apple, decides to take part of that encoding space for their own instructions... do you see the implications? Now, that space is unavailable to ARM. ARM, the owner and custodian of the ISA, are put in an impossible position: accept those instructions into the ISA (if Apple allows it, because now it's their IP) or lose unity in their ecosystem (fragmentation). In any case, they've lost extremely valuable encoding space and, more importantly, control over their own ISA.

And that's why not only ARM don't allow licensees to implement their own instructions, they will never allow it (generally speaking; they have reserved some encoding space in the M profile for custom instructions, but that's controlled customization in a profile that has fewer instructions to begin with).

Thanks. Makes a lot of sense.

Apple is making a really strong push to differentiate it's chips from ARM. A few of the mac sites are claiming it's "Apple Silicon" and not "ARM". I believe the heart of it is that Apple has "followed the ARM spec" but did not use ARMs actual silicon designs.

I don't really know what the backing of this is either. I'm sure they added a few of their own instructions. And I read that they single handedly pushed the ARM platform to 64bit (citation needed, definitely not sure if that's really true).

"Apple Silicon" is a literal truth. The silicon design, the microarchitecture, is theirs, not ARM's. The architecture, this includes the ISA but also many other things that have to be taken into consideration in CPU design (exception model, consistency, virtual memory, virtualization,...), is ARM's. They simply don't want to tie their brand to ARM's, which is fair enough, Apple's brand is much more valuable than ARM's.

Regarding the push for a 64-bit chip, I've heard the exact opposite. Aarch64 (64-bit ARM) was an ARM design without a customer, Apple were the first to buy into it. I've heard that many said it was a premature jump, and there was a lot of scepticism within ARM that they'd be able to sell it (this happened when ARM was selling mobile designs exclusively, with no intentions of getting into servers). Still, they went ahead with it, and was an unexpected success.

It’s easier to just tweak some system registers than to do that (and indeed this is how Apple implements their proprietary “in-silicon” features).

HN seems to dislike too much conciseness -- I guess a single-word comment, even if it's a good reply, comes across as impolite or low effort (for the lack of tone in text).

Thanks. (Please don't downvote me!)