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Comment by redshirt | Hacker News Reader

They don’t have full control. Apple can’t add instructions, only Arm can. If they want something new they have to go back to Arm, sure hey probably have lots of pull, but that’s the way it is. And one reason ppl like RiscV.

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Actually - if I'm not mistaken - what you say holds true for almost any other company but _not_ for Apple: They are holders of an architectural license, which gives them (and very few others in the world) this freedom.

It was discussed a while ago here on HN: https://news.ycombinator.com/item?id=10190521

Architecture license means you can use the ISA (provided by Arm). Micro arch means you can license the core implementations form Arm. Apple is an ISA license, meaning they have full control of the micro arch as long as it passes verification by Arm. That’s the beauty of Arm, you get rid of the problem of creating the whole software ecosystem...it’s already there, and companies like Cavium, Apple, Qualcomm are free to add their secret sauce and benefit from the mature software environment. At least, that’s the hope.

Prior to ARMv8, all licensees could add additional specialized instructions or even entire instruction sets using the ARM coprocessor model.

By changing a few registers, you could alter how instructions were interpreted. This was used by some vendors for hardware-software interfacing, and by others to provide specific acceleration primitives for their specialized workloads.

ARM used this mechanism themselves to offer an optional floating point unit, with specialized vectorized floating point instructions.

Unfortunately, support for coprocessors has been removed from ARMv8.

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