[simondotau]

In order for an Apple Silicon Mac Pro to make any sense whatsoever, its SOC will need have to have support for off-package memory and substantially more PCI-E lanes than the M1 Ultra. Therefore it seems all but certain to me that it will debut the M2 chip family.

Apple isn't going to give up the substantial performance benefits of on-package unified memory in order to support DIMMs. Therefore I predict that we'll see a two-tier memory architecture with the OS making automated decisions based on memory pressure, as well as new APIs to allocate memory with a preference for capacity or performance.

The chassis design is new enough that it was designed with an eventual Apple Silicon Mac Pro in mind, so I expect to see minimal change to the exterior. It might shrink and have fewer slots (particularly since most users won't need a slotted GPU) though I think that's unlikely given that its height and width was defined by 5U rack dimensions.

[kimixa]

Currently the performance and power benefits of having tightly packaged RAM are taken full advantage of by the M1 family. A less tightly coupled memory system will likely have significant performance implications. There's a reason why all GDDR memory for GPUs is soldered, as there's signaling issues caused by things like longer traces and the electrical behavior of the sockets themselves.

People also seem often to forget that interconnects are a significant amount of modern power budgets - look at the Epic IO die often using more than the cores in many workloads. It may be the the M1 family looks less attractive when you actually have to add these requirements.

Perhaps there's some possibility of having both a tightly-coupled RAM package and also have an extensible memory system - though that has significant management complexity if you try to treat it like a cache, or likely needs app support if it's some NUMA system where they're mapped separately. But possible, at "just" the cost of the extra memory controller.

[ksec]

I would love to be wrong but I dont think DIMM will be a thing on Mac any more. Not only does it not make economical sense for Apple with additional DDR5 memory controller support and testing, they can now also charge substantial premium for memory.

[structural]

DIMMs likely won't be a thing anywhere before too long. They're too large and problematic to deal with for the latest memory interfaces (which previously had only been found on GPUs). There's only so much you can miniaturize before the connectors become a real problem - and we can now put an entire "computer" in a single package.

I'm interested to see when the PC form factor goes away completely, likely 1-2 generations of product from now.