[joshpadnick]

Naive but genuine question: What are the major advantages of switching to an ARM processor? From Apple’s keynote, I gathered that there’s the benefit of instant-on, and allowing iPhone/iPad apps to just work in MacOS, but are there some other fundamental advantages to be had with ARM for Mac? What difference does it make for both power users and real consumers at the end of the day?

[sgerenser]

Another big one: not relying on 1 or 2 large companies for CPUs. Intel and especially AMD can’t afford to make (what they perceive to be) niche features on their CPUs. They have to design for the mass market, or if offering something more unusual or specialized they have to sell them at very high prices.

With ARM, any company is able to get an architecture license and go hog wild. The architecture (sticking to AArch64 since nobody cares about 32 bit ARM anymore for general purpose computing) is much cleaner and simpler with less cruft than x86. This makes it easier for a variety of companies to offer different solutions at different price, performance, and power points. Plus with the weight of Apple behind it there will surely be much more development in both the ARM software and hardware space as it applies to general purpose desktop computing.

[oblio]

Yeah, but Apple's stuff won't necessarily translate to generic ARM, they have their own extensions. Plus their own OSes.

I don't really see how this benefits Linux or Windows.

[sgerenser]

They have their own extensions, but having a mainstream desktop platform that runs on ARM will certainly be a push for compilers and software to have better support for ARM in general. For example, right now Docker ARM images are basically an afterthought and if something doesn't work in the ARM version a maintainer might just shrug their shoulders and view ARM as a niche use case. With a critical mass of ARM desktops that will no longer be the case.

[spijdar]

The benefits don't really have that much to do with ARM specifically, more that Apple can tune their silicon designs for their very niche applications, while ARM Holdings designs and other silicon IP designers have to design much more generally as they're selling to a broader customer base integrating the cores into everything from smartphones to edge switches.

I'm not sure to what extent they've done so, but with their own silicon Apple has the freedom to simply not implement the unnecessary optional bits of ARM, like 32 bit support, and the optional extensions to the ISA not applicable to desktop class general purpose compute.

The saved space in transistor budget could allow them to save precious time and energy in performance critical spaces like the instruction decoder/fetcher.

No idea what they're actually doing (they're not exactly very open about their designs) but with their own processors they're free to optimize for a specific use case and a specific kernel. A specific example of this is how they've reduced the time spent in garbage collection by a factor of 3-5 IIRC, which has pretty dramatic ramifications for both performance and memory usage (as you can do GC quicker and more often)

[klelatti]

Just a few clarifications:

- M1 is indeed 64 bit only

- Apple's software doesn't use GC - it uses reference counting which has indeed been speeded up dramatically.

The M1's (two) CPU designs are Apple's own and there is a lot of information out there on them e.g.

https://www.anandtech.com/show/16226/apple-silicon-m1-a14-de...

[spijdar]

Thanks for the info :)

I counted ARC as a sort of GC, though I've heard the opinion it is and isn't a type of GC, and see both sides' points

I love that article and the research behind it, but it's worth pointing out the details are sort of "reverse engineered" by probing XNU and running some diagnostic programs, not from apple supplied docs. I doubt apple will ever directly document it like IBM or Intel document their CPUs, though I hope I'm wrong!

[klelatti]

It's a great piece and as you say it's a shame that we won't see more detailed info from Apple but I've seen a couple of interesting comments (leaks?) from Apple employees with more details (e.g. the tweets embedded in the article below). I suspect that we'll know an awful lot about the M1 by the time we've finished!

https://blog.metaobject.com/2020/11/m1-memory-and-performanc...

[lbotos]

For Apple, deeper control of their vertically integrated stack. Which depending on who you ask, is a good or bad thing.

Other commenters here covered other benefits as well.

[mlacks]

Longer battery life for individual consumers, cheaper electricity bills at scale