ARM Wrestling

We're coming up on WWDC, and in an eerily similar way, the imminent announcement of a transition of the Mac line to a new processor architecture is being reported in a big mainstream newspaper. This time, we're talking ARM Macs in 2021.

There are many questions to ponder:

What about the Mac Pro?

Given that the Apple A series of processors are so ahead of other ARM processors that flagship Android devices released recently are having trouble keeping up with last year's Apple counterpart, I don't think there's an issue achieving performance in the abstract. The ARM architecture has always been famous for its power-sipping, to the point where during the first successful power-on, it was able to run without the power supply being properly hooked up, and Apple's work with thousands of independent power domains to power only the parts of the chips that are necessary at the moment doesn't exactly hurt.

This doesn't mean it's easy to scale up in a smart way, that can compete with Xeons and especially modern AMDs. But the story of ARM over the years has been that it's much easier to make it go fast than an x86 family CPU power efficient.

PCI Express is strongly entangled with the idea of a modular PC, but the standard is its own island. There's no reason an ARM Mac Pro can't have just as many (or more) PCI Express slots or interfaces.

But a new CPU brings with it an entirely new environment, though. The boot environment of the new Macs are much more likely to be based on T2-style security. UEFI is available on ARM, but Apple is essentially starting over no matter what. On top of this, the software stack, the OS and the access allowed can be wildly different architecturally. Being able to stick in a PCI Express module doesn't mean all assumptions will hold about how to work with it. The compatibility story for GPUs will be especially interesting, since Apple's GPU chops are much more untested than their CPU chops.

Even if all of these are handled in the most inclusive way possible, unless there's some sort of extra bone thrown towards Mac Pro users, who now have seen a platform long-neglected, then ostensibly rebooted, twice, back-to-back, the future for the Mac Pro as the value proposition it currently occupies is murky at best. Forming a Pro team and taking everybody out for a ride of gradually coming to terms with actual people's actual needs only to decide that they are no longer a priority would be unspeakably stupid. Unless Mac Pros will live on in the current form, there's more to this, although maybe not revealed immediately at this year's WWDC.

With USB4 subsuming Thunderbolt 3, it's not impossible that Mac Pro could just get AMD's best performing CPUs in them and gain an impressive boost. (Although there's other Intel technology to worry about, such as the wireless video standard one that powers Sidecar.)

What about the software story?

macOS is not going anywhere. It would be criminally incompetent to assume that only UIKit/Catalyst-based apps were welcome on ARM Macs. Apple would have to rewrite, to a first approximation, all of their own software for that to fly, including Finder, Safari and all Pro apps. Macs will still be Macs, at least in that regard.

What might happen is that, as has happened with 32-bit-to-64-bit transitions before, chunks of the platform that's being supported and maintained largely for compatibility is unceremoniously sloughed off. With the decade-long trend towards sandboxing, "Developer ID" and notarization, I'm feeling ill at ease for what could be made to be mandatory. I don't think it will be bad enough that the Mac App Store will turn into the only mode of distribution, but if they ever wanted to do it and anchor it in some technical credibility, now would be the time.

Of course, there's nothing inherent about ARM itself that makes this inevitable. Looking back, it's been more prevalent across ARM devices simply because they've been devices - which are expected to perform a set function first, and where some lockdown to ensure the stability of that function is at least straightforward to motivate. But one of the most widely known ARM devices today is the Raspberry Pi computer, which is the epitome of hackable and open and free from such lockdowns. A general-purpose computer is still closer on the scale to a Pi than an iPad. Being able to bring out the power tools when necessary isn't an obstruction of the function, but rather a part of the function itself.

What about all the little stuff?

The hardware "form factors" that can be brought to market using ARM are worth considering.

  • A Mac mini that looks more like, and develops about as much heat and fan noise as, an Apple TV; similar in size to a NUC, and much more similar in price.

  • A MacBook that out-MacBook (2015)s the MacBook (2015). Lower power consumption means less cooling and less thermal throttling, and much less batteries – and much less weight and volume/thickness.

  • A Mac Pro mini, with the best performing chip they can put in there, an onboard AMD GPU, iMac-level SSD storage and user-replaceable RAM. Think the Mac Pro without the PCI Express slots, and likely the size of the G4 Cube. It's not a bad concept (it's just horrible when it's the complete extent of the platform). This is possible with Intel today, but cooling and power draw would likely make it too bulky to be tiny, or bring down the level of performance by a lot. Pro products never used the energy-efficient Core chips, and the G5 was a famously bad fit, so this might be the first time it's considered worth doing again by the powers that be.

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