Musings on the unreleased Apple Silicon Pro Macs

So far, the Apple Silicon (AS) macs released have all been low-end machines. The M1 SOC powering them is effectively a beefed up version of the A14 chip in the iPhone 12. it has double the number of performance CPU cores, a larger GPU and a thunderbolt controller. The RAM is packaged with the SOC (in a very ipad-like way) and there’s 8GB and 16GB configs. Being part of the SOC package, obviously there’s no way to expand it later. It’s a pretty powerful chip, especially compared to what it’s replacing, and it’s very power efficient – helped by the 5nm process it’s built on. But it’s also clearly a limited design for high-end use. So Apple-watchers and pro users like me are very interested to see what kind of hardware design they’re going to create for the mid and high-end Macs. The M1 was pretty much exactly what I expected (apart from it being built on 5nm) but it’s a lot harder to guess what they’ll do to compete with higher-spec PCs running discrete graphics from AMD and Nvidia.

So here’s my predictions. The next machines to be unveiled (likely at WWDC) will be the new Pro iMacs and new high-end MacBook Pros. The iMacs will definitely have a new form factor – maybe losing the “chin” of the existing design (though the low-end Apple Silicon iMacs belie that idea), and a narrower iPad-like bezel around the edge of the screen. The MacBook Pros will largely look the same as the existing ones, though there are rumours they may lose the Touch Bar and bring back physical function keys abd MagSafe power(which would make me happy). The form factor is the least interesting part of it though. I suspect these machines are going to be based on two new SOCs. They will not support expandable RAM – you will have the choice of RAM configs at purchase, which I suspect will be: iMac – 16GB, 32GB, 64GB or 128GB, MBP – 16GB or 32GB. The RAM itself may not be actually built into the SOC package as it is in the M1, but it will be set around the SOC in a tightly coupled arrangement, similar to the ones in the Xbox Series X and Playstation 5.

One thing Apple has repeatedly touted as an advantage of the M1 (and their A series SOCs) is the unified memory architecture. All components in the SOC – CPUs, GPU and Neural Engine – have access to the same flat memory model. This provides a huge performance boost for mixed code that needs to be run across different types of functional hardware sharing the same assets in memory. The problem is, this only works with their own GPU designs right now. There’s no way to add a discrete GPU, which by its nature has a separate memory pool. And while Apple’s GPUs are decent compared to many mobile devices, they don’t come anywhere near the performance of AMD and Nvidia’s current-gen GPUs. Not to mention that they lack any form of raytracing hardware – which will increasingly be seen as a key visual differentiator in game graphics (and has huge advantages for pro apps too).

So what I think they’re going to build – certainly for the iMacs – is a SOC more akin to the ones in the PS5 and Xbox Series X. And I reckon they’ve been working with AMD on it too. I think the “M1 Pro” (henceforth referred to as M1P) will still be based in part on the A14 architecture, but with 6-8 high performance cores and with fewer (or no) efficiency cores. It could have an expanded neural engine, but the most interesting part is the GPU. I can’t see apple putting a discrete GPU in there, so what I think they are going to do is license an AMD GPU based on Big Navi and have it integrated into the SOC. AMD and Apple’s engineers will have worked to make this variant of Big Navi work with the unified memory controller of the M1P.

For expansion, this SOC will have 24 lanes of external PCI-E 4.0, which will enable at least 4 thunderbolt/USB4 ports as well as supporting other hardware like 10GB ethernet. The SOC will – like all other Apple SOCs – connect to Flash storage using a dedicated flash controller onboard. I would be interested to see if they will support internal storage expansion via a M2 card, but I suspect that it will more likely be either a custom module, or actually soldered onto the motherboard.

The MacBook Pro (high end) presents an interesting challenge. I suspect the M1P I’ve described above will be too large for a laptop, in terms of power usage and thermals. So the SOC powering it will either be a cut-down version of the M1P, with a smaller AMD GPU and fewer performance cores but bringing back more efficiency ones. Or it might be a beefed-up version of the existing M1, using an Apple GPU design, but with more cores.

Much further down the line, we will eventually see the Mac Pro replacement. This presents a very interesting challenge for Apple’s engineers. The Mac Pro user base expects things like PCI-E slots and expandable RAM configurations. I honestly don’t know how Apple will reconcile this with their SOC approach for all their other Macs. I suspect there may be an even higher end configuration of the M1P created with 64 or more lanes of PCI-E 4.0 and socketed RAM in user-configurable arrangements. This does get messy from an engineering perspective though and will exact a memory performance penalty. As a result, I wouldn’t even be entirely surprised to see Apple create their custom memory modules, which will no doubt be eye-wateringly expensive (though fast!) – rather than using standard DIMMs.