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Comment by tambourine_man | Hacker News Reader

What you’re describing is the iMac, iMac Pro, Mac mini pro, etc.

But I think they’ll have the Mac Pro continue to be RAM, GPU and PCI upgradable.

How they are doing that is the most interesting secret in the industry.

There's not really any magic to it, they just need to implement PCIe and include memory slots instead of hardwired chips on the package. There are other ARM systems that already do this.

Yeah, but then you lose the benefits of the integrated memeory.

How they're gonna solve that is the big question.

There actually aren't really any benefits outside of manufacturing. Trace length is a marginal factor in memory performance/latency, and having the memory on-package versus only slightly further away doesn't mean much. I'm not sure exactly where the idea that having the memory on-package was so beneficial came from, especially considering the M1 actually has fairly poor memory latency (though within the expected normal range for LPDDR4X):

https://www.anandtech.com/show/16252/mac-mini-apple-m1-teste...

As far as HSA/unified memory architecture, PCIe 4.0 has enough bandwidth to comfortably access main memory for applications that support it (and vice versa with GPU memory), although I imagine most high-performance GPU workloads will do better primarily operating on dedicated GPU memory (especially given that a single M1 core can already saturate the memory controller on its own).

This is not my area of expertise, but I’ve seen concerns of implementing the unified memory architecture off chip. But maybe it’s just that it hasn’t been done yet.

That doesn't have any impact. The memory isn't on-chip, it's just on-package. This makes it no different from if it was fully external.

This has also not been a problem for any other unified memory system (which typically also do not include memory on-package), and I can't see any reason why it would matter.

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