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Xeons have many, many PCIe lanes. Apple Silicon only needs enough HSIO for SSD and Thunderbolt ports, and they’ve released all of the non-internally-expandable

Xeons have many, many PCIe lanes. Apple Silicon only needs enough HSIO for SSD and Thunderbolt ports, and they’ve released all of the non-internally-expandable machines already. They needed a chip that added 48+ PCIe lanes to the package so they could satisfy the relatively few Mac Pro customers. And without external DRAM, they’ll never be able to provide as much memory as a low-end Intel chip in the Mac mini at the same price point. In-package DRAM is better performing but it changes the price/perf graph. Apple simply optimized their silicon packages for 90% (or more?) of their users over the outliers.

eyelidlessness 4y ago
There’s some very interesting speculation on the ArsTechnica forums about how expandable RAM on a Mac Pro might look. It’s not my speculation but it’s definitely not all said and done from what I’ve read.
- blkhp19 4y ago
  Any links?
mrtksn 4y ago
Considering that Mac Pro is a special purpose machine, maybe it can be possible to have an architecture with multiple M2 Ultra chips and expansion options for special purpose hardware? Highly parallelizable workloads and use cases with special hardware requirements(like encoding media, ML computations etc.) can benefit from this stuff. Apple already sells cards like this for Mac Pro. Surely that would require architectural changes and the software would need to be adapted but since these machines are niche, so is the software and Apple can sponsor the development of the few software people are using on that kind of machines. Apple is sponsoring Blender for example.
- zozbot234 4y ago
  Well, the Ultra is already multiple silicon dies (chiplets) on an interposer. So this would have to be multiple packages, sitting in separate sockets on the same logic board. I agree that this seems like it could be a viable strategy to get around any packaging constraints that they might have.
- silvestrov 4y ago
  I see 3 steps: a) Mac Studio, b) MacPro with PCI/MPX modules, c) Dedicated HW boxes. I think the size of the step between a and b is becoming too small to be viable: not enough extra performance, and too high price compared to step c. Dedicated HW boxes connected using Ethernet/Thunderbolt/USB-C have the great advantage that you are no longer bound to whatever Apple offers this year. You will just use the Mac/Windows as a "advanced graphical terminal". Same for hardware developers. Looking back at the past 10 years of MacPro shows great uncertainties in what Apple offers going forward. Why would you spend time making a PCI card for MacPro when Apple so easily abandons support for PCI with the TrashCan while you could have a reliable market with a thunderbolt/ethernet accessory?
NathanielK 4y ago
The on package DRAM for the current macs isn't anything special. It's just normal LPDDR running at normal LPDDDR speeds, same thing you find in your phone. On package has many advantages, but it's not a hard requirement. The bigger is how much LPDDR5 memory they can hook up to their 512bit memory controller.
- nine_k 4y ago
  Maybe the very ability to make a 512 bit-wide memory controller stems from the very short, very tightly controlled and shielded lined between the DRAM chips and the controller? (No idea if it's so, but DRAM is such an analog HF beast that a controller needs training before it can work with a particular chip, in a particular slot on a particular system board. It's automatic but it's there, and it must have limits.)
  - MrBuddyCasino 4y ago
    High end graphics cards have been using 512 Bit wide memory buses for a while, so I don't think that's it.
    - pornel 4y ago
      but the GPU RAM is not expandable and seems to be a big price factor.
novok 4y ago
IMO I think the reason why they didn't release the M1 Pro mini is because they didn't want to cannibalize their mac studio release. The M1 mini chassis has a ton of empty space, and the m1 pro is easily cooled by that space and is already cooled fine by the tiny macbook pro coolers, which also means an M1 Max mini would've worked fine also. IMO the M1 Max studio body is unnecessary too, it's only really needed for the M1 Ultra, which would lead to barely anyone buying the mac studio form factor.

eyelidlessness 4y ago

There’s some very interesting speculation on the ArsTechnica forums about how expandable RAM on a Mac Pro might look. It’s not my speculation but it’s definitely not all said and done from what I’ve read.

blkhp19 4y ago
Any links?

mrtksn 4y ago

Considering that Mac Pro is a special purpose machine, maybe it can be possible to have an architecture with multiple M2 Ultra chips and expansion options for special purpose hardware? Highly parallelizable workloads and use cases with special hardware requirements(like encoding media, ML computations etc.) can benefit from this stuff. Apple already sells cards like this for Mac Pro. Surely that would require architectural changes and the software would need to be adapted but since these machines are niche, so is the software and Apple can sponsor the development of the few software people are using on that kind of machines. Apple is sponsoring Blender for example.

zozbot234 4y ago
Well, the Ultra is already multiple silicon dies (chiplets) on an interposer. So this would have to be multiple packages, sitting in separate sockets on the same logic board. I agree that this seems like it could be a viable strategy to get around any packaging constraints that they might have.
silvestrov 4y ago
I see 3 steps: a) Mac Studio, b) MacPro with PCI/MPX modules, c) Dedicated HW boxes. I think the size of the step between a and b is becoming too small to be viable: not enough extra performance, and too high price compared to step c. Dedicated HW boxes connected using Ethernet/Thunderbolt/USB-C have the great advantage that you are no longer bound to whatever Apple offers this year. You will just use the Mac/Windows as a "advanced graphical terminal". Same for hardware developers. Looking back at the past 10 years of MacPro shows great uncertainties in what Apple offers going forward. Why would you spend time making a PCI card for MacPro when Apple so easily abandons support for PCI with the TrashCan while you could have a reliable market with a thunderbolt/ethernet accessory?

NathanielK 4y ago

The on package DRAM for the current macs isn't anything special. It's just normal LPDDR running at normal LPDDDR speeds, same thing you find in your phone. On package has many advantages, but it's not a hard requirement. The bigger is how much LPDDR5 memory they can hook up to their 512bit memory controller.

nine_k 4y ago
Maybe the very ability to make a 512 bit-wide memory controller stems from the very short, very tightly controlled and shielded lined between the DRAM chips and the controller? (No idea if it's so, but DRAM is such an analog HF beast that a controller needs training before it can work with a particular chip, in a particular slot on a particular system board. It's automatic but it's there, and it must have limits.)
- MrBuddyCasino 4y ago
  High end graphics cards have been using 512 Bit wide memory buses for a while, so I don't think that's it.
  - pornel 4y ago
    but the GPU RAM is not expandable and seems to be a big price factor.

novok 4y ago

IMO I think the reason why they didn't release the M1 Pro mini is because they didn't want to cannibalize their mac studio release. The M1 mini chassis has a ton of empty space, and the m1 pro is easily cooled by that space and is already cooled fine by the tiny macbook pro coolers, which also means an M1 Max mini would've worked fine also. IMO the M1 Max studio body is unnecessary too, it's only really needed for the M1 Ultra, which would lead to barely anyone buying the mac studio form factor.