Looking Ahead to 2023 pt 1

[melgross]

Very interesting article.

I would like to say one thing about the possible Mac Pro. I seem to read everywhere that it’s impossible to add RAM to Apple’s SoC modules. I’d like to differ. I’ve been saying this for some time. The RAM packages are on the substrate, which is a special type of small board that Apple’s SoC and memory modules are on. They are not part of the SoC. Apple is not the only company to use substrates. The way Apple does this is obvious. They pull all the needed lines to the memory out of the chip to the sides of the substrate where the RAM packages are. Apple uses either two or four packages, depending on the chip, and different capacity packages as well.

As far as I know, there’s no reason that Apple, if they wanted to, couldn’t have small sockets for those packages on a slightly larger substrate. Then other RAM packages could be inserted, if they support these lines. Empty sockets could also be provided for additional packages. From examining what we know about Apple’s chips, I can’t find a reason why Apple couldn’t do this - if they so desired. Apple’s “fabric” as they call it, can accommodate whatever configuration they want it to. The question here is whether they would want to either customize a chip design solely for the smaller sales of a Mac Pro, or possibly even have this as a next generation chip design, perhaps led by it first being implemented on the most expensive model, the Mac Pro.

From what I’m told from some people who have some idea as to what Apple is doing, the M3, done on the 3nm line at TSMC is going to be a significant upgrade. It will be interesting to find out what that is.

And, by the way, assuming a bit of increase in lag is acceptable, GPUs could be added in this way as well.

[danfried2]

You're quite correct that the M1 and its variations are a MCM (Multi-Chip-Module). However, the substrate for that MCM, with its components soldered to it, is then encapsulated in a package with a thermal connection to the heat management system. While there are 3, or more, chips in the MCM package, it is still only 1 package and, from the outside, will appear as a single device. To bring the memory connections out of that package would significantly increase the trace length and therefore the capacitance of each trace which slow down the system and increase power consumption - a bigger problem than in traditional architectures because this memory functions as RAM, GPU memory and storage. Yes, it would be great to be able to add memory in the future, but the architectural design, even though the memory chips are physically separate on that common substrate with the Mx processor, will probably not permit that. All that said, perhaps the mother board could be designed such that the entire MCM could be replaced with a more advanced one in the future. I believe that the MCM is socketed. So, would I be able to replace the M1 Max in my Studio with a M3 Max in the future??