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Note that the biggest customer/developer pain from the PPC->Intel and Intel->AS transitions are not the CPUs themselves per se, but the ISA changes.

Apple's current arrangement is that they license the rights to the ISA, but have the freedom to do whatever they want in their CPU designs. And they do. They have their own "from scratch" ARM CPU cores much in the same way AMD has "from scratch" x86 CPU cores.

Being able to leverage an existing ISA, but design their own architecture backing that ISA prevents iOS from going through one of these ISA shifts when Apple started replacing reference designs with their custom designs, so it makes sense for Apple to license the ISA like they do. Any future ISA shift will very likely affect the Apple's whole product line, so there is a bit of a disincentive to do one so quickly after migrating the Mac. It's not exactly cheap on Apple's part to provide test hardware, transition bridges like Rosetta, burning goodwill they've built up, etc.



I'd be surprised if Apple switches ISAs anytime soon, though. While they don't need anything from ARM, they have a very practical arrangement that has benefits for Apple. So Apple does have an interest to prod future ISA additions and changes in a direction that benefits them as long as they can maintain a good working relationship.

Why do they need "Arm Cores" ?
If they don't need ARM and design their own silicon genuinely from the ground up, then they don't need to copy? anything from ARM whatsoever do they?
 
Why do they need "Arm Cores" ?
If they don't need ARM and design their own silicon genuinely from the ground up, then they don't need to copy? anything from ARM whatsoever do they?

They use the ARM ISA for their CPU cores. That requires a license to do, since the ISA is proprietary. AMD has a similar license for x86 from Intel, and Intel for x86-64 from AMD. It doesn’t matter that Apple doesn’t use ARM’s core designs. AMD/Intel don’t use each other’s CPU designs either, despite using the same base ISAs, but they are still dependent on each other for those licenses.

Think of the ISA as the “standard”, and the CPU core design as the ”implementation of the standard”.

The key here is that what makes an architecture switch expensive is the switch of the “standard”. That’s what requires software to need translation and recompilation. So there’s an incentive for Apple to minimize how frequently they make these big sort of changes, even when they design their own silicon. The rumor is that they were involved in the work behind the ARM64 ISA, which if true, lends some weight to the idea that Apple would rather try to steer ARM ISA development when it matters than jump ship to their own ISA, at least for now.

EDIT: If Apple really felt like they needed to go 100% solo, the time to do so was with the M1.
 
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They use the ARM ISA for their CPU cores. That requires a license to do, since the ISA is proprietary. AMD has a similar license for x86 from Intel, and Intel for x86-64 from AMD. It doesn’t matter that Apple doesn’t use ARM’s core designs. AMD/Intel don’t use each other’s CPU designs either, despite using the same base ISAs, but they are still dependent on each other for those licenses.

Think of the ISA as the “standard”, and the CPU core design as the ”implementation of the standard”.

The key here is that what makes an architecture switch expensive is the switch of the “standard”. That’s what requires software to need translation and recompilation. So there’s an incentive for Apple to minimize how frequently they make these big sort of changes, even when they design their own silicon. The rumor is that they were involved in the work behind the ARM64 ISA, which if true, lends some weight to the idea that Apple would rather try to steer ARM ISA development when it matters than jump ship to their own ISA, at least for now.

EDIT: If Apple really felt like they needed to go 100% solo, the time to do so was with the M1.

I disagree with your last point. Doing it when the did the M1 would mean that in addition to all the other changes in system architecture, they’d have to deal with a new, untested, ISA. When they eventually do it, the iphone, ipad, Apple Watch, etc. will go along in lock-step. And it will likely be evolutionary, not a complete rip-out of all Arm64 instructions all at once.
 
I disagree with your last point. Doing it when the did the M1 would mean that in addition to all the other changes in system architecture, they’d have to deal with a new, untested, ISA. When they eventually do it, the iphone, ipad, Apple Watch, etc. will go along in lock-step. And it will likely be evolutionary, not a complete rip-out of all Arm64 instructions all at once.

I agree that an ISA change is something Apple is best served by doing it across their SoC range. But I still think the point stands that the best opportunity to take such a leap is when you are already taking the leap for other reasons.

Apple could go with a mixed-mode CPU similar to the 64-bit transition, but that really allows the transition to run longer. It doesn’t really reduce the costs or the fact that you’re shifting the ISA. And much like the 64-bit transition, such a switch would act to encourage developers to lag behind unless given the stick. But depending on where Apple’s interests lie, there’s still quite a bit they can do by adding extensions on top of ARM64, and custom ASICs like the neural engine rather than going it alone. AMD and Intel have both been playing that particular game for a number of years at this point.

But as I’ve said before, my expectation isn’t so much that Apple won’t go it alone, but rather such a shift is quite a long ways off.
 
Proposed acquisition of ARM Limited by NVIDIA Corporation: public interest intervention
Under the powers set out in the Enterprise Act 2002, the Secretary of State for Digital, Culture, Media and Sport is able to intervene on national security grounds. This responsibility is discharged in a quasi-judicial capacity.

On 19 April 2021, the Secretary of State issued a public interest intervention notice (PIIN), confirming that he is intervening in the sale on national security grounds. In reaching this decision, he considered advice received from officials across the investment security community.

The Competition and Markets Authority (CMA) will prepare a report on the competition and national security aspects of the proposed transaction. The CMA has until midnight on 30 July 2021 to complete and submit this report to the Secretary of State.
 
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