programmer

Apple exec makes evasive statements about undisclosed products. Shocker! The highest end product is always going to be the most challenging one to build, not the least because of the expectations (unrealistic or otherwise). Apple is taking its time to build a product that it thinks will be worth putting into the marketplace… otherwise why do it? It will never be what fanboy imaginations can dream up because of engineering and financial realities. It can still be a great product with a solid target market. And it may take a while for it to materialize.

mattinoz said:

Why is PCIe unlikely? You are stating that but none of the rumoured information has been anything other than speculation that looks like it is trying to drive negative sentiment. Also the two year wasn't a deadline as the direct quote is "about 2 years" which makes this feel like an attempt to also drive such negative sentiment more than speculation based on the new information. Indeed a reference of a Compute Module does suggest Apple does have the ability to move the ASi SOC off the mainboard into a pluggable object which would kind of make sense to be Apples already designed MPX. Leading to more to the inclusion of PCIe not dissimilar to current intel MAC pro more than it supports "PCIe being unlikely" Make sense that Apple have been waiting for PCIe 5.0 CXL support in ARM so 3rd parties have a more attractive target.

Note that the article says "PCI-E GPUs", not any "PCI-E".  Plenty of discussion in other threads why GPU support (at least for the purposes of doing graphics) may be unlikely/complicated.  

That this was found in iOS seems to make it unlikely to be Mac Pro specific, but it does make me wonder if Apple is looking toward a future where there is a software fabric that allows connected devices (via network, PCI-E, whatever) to share compute.  There has been some work done in the past (grid computing), and existing product (xcode's distributed builds), and cloud services (some Siri compute is offloaded).  Or the Apple Watch and iPhone sharing workloads.  

If having such a generic mechanism available is something they are working on, then letting iOS devices make use of it does make a lot of sense.  And a headless compute device could run iOS instead of (or in addition to) macOS, especially if it can run workloads from either platform.  The result could be standalone devices (e.g. a Mac mini without anything connected except power and possibly Ethernet), or add-in boards for a Mac Pro chassis (e.g. M2 PCI-E cards).  Such a technology would be hard to make use of transparently and would require developer support in their applications... either directly or via APIs they are already using (e.g. the ML libraries Apple introduced in the past few years).  

Distributed computing has become much more feasible in the past decade or so because of the speed and ubiquity of networks and interconnects, and the existence of heavy compute workloads.  And if more small wearable devices (e.g. AR glasses) are on the way but keep their compute capability to a minimum for size/weight/battery reasons, then having a compute device to support them could make sense (e.g. much like a phone does for the watch but without the power draining display which might be redundant due to the other wearable(s)).

Plenty of room for speculation.    

mattinoz said:

When was the last time Apple went alone on such a low level system and it paid off?
It has been awhile. 

If they are going something new then it would be new thing the industry is abuzz with better still if they can contribute too. 
Apple have said they will only do their own where they can do better for Mac Pro even a MacStudio they can't do better they need to open the door.

Well... Apple Silicon itself is such a "low level system".  On one hand, I agree that I don't think we will see Apple create an "all singing, all dancing" board level interconnect.  On the other hand, that isn't what is needed here.  They did the edge connect between 2 M1 Max chips to produce the M1 Ultra, not to mention the on-SoC network in their silicon itself... so there is some indication that they are willing to work in this space.  Realistically, they're going to have to do something because chiplet-based SoCs are where the industry seems to be going.  At the chiplet in-package level, I think we could see Apple do something, but at the board level, I doubt it.  They'd probably just use the latest PCI-E, or perhaps even license a fabric from someone.  If both sides of the connection aren't Apple Silicon, its going to be an industry standard interconnect (PCI-E).  If both sides are Apple Silicon, it looks like that will only be an in-package interconnect.  An Apple Silicon to Apple Silicon interconnect at the board level would be a surprise, and would (almost certainly) be unique to Mac Pro... and thus not worth them investing enormously into a hugely expensive R&D effort.  So if the Mac Pro does contain multiple AS packages (and I'm doubting it), I would expect an off-the-shelf interconnect (most likely PCI-E as they already have it in their hardware, but they could also license something else).  In the short term, therefore, I expect M2 Ultra.  In the M3 timeframe, bigger packages.  Beyond that, its too hard to predict.

The original post and none of the subsequent posts mention what is almost certainly the biggest stumbling block to supporting non-Apple GPU hardware:  drivers.

Drivers have always been the biggest issue with Apple GPU support, and it has always been a hot potato tossed back and forth between Apple's OS group and the 3rd party HW vendor (including Intel for the integrated GPUs).  GPU drivers are terribly complex things, and Apple can't/doesn't use the drivers written by AMD/Intel/nVidia... and those vendors aren't likely to put much effort into writing drivers for macOS even if Apple were to start shipping their GPUs in Apple products.  They never did before, the market is too small.  So will Apple write drivers for any 3rd party devices?  Their current direction suggests that the answer is a resounding "no", but that's not definitive and could change.  They still have drivers that work on the Intel chip based Macs, and porting to Aarch64 may not be terribly difficult.  Keeping up with the moving target that is the latest AMD GPUs though, is a lot of work.  On top of supporting Apple's own GPU designs.  

The Apple Silicon hardware is almost certainly hardware compatible with most GPUs from other vendors, thanks to PCI-e / Thunderbolt being standardized in its various flavours.  So you can physical install any of the devices, but you need drivers to make it interoperate with macOS and macOS needs to continue to expose the functionality required to do that (which conceivably it may not on Apple Silicon since the macOS team may be taking advantage of detailed knowledge of the hardware).

cgWerks said:

Of course, as the article points out, there are benefits as well. Maybe Apple’s memory architecture reduces the downsides. But, unless the industry shifts, the benchmark will be the PC systems, and Apple’s systems will be criticized on situations where they can’t keep up. (ex: the article talked about high-complexity scenes, for example, where TBR isn’t as good.)

This is always a risk of doing things differently.  Particularly if the different approach requires different software.  Apple's approach may be as good (or better, even) than everyone else's, but if it requires software devs to "think different" in order to realize that advantage, then Apple is going to get criticized over it.  This may or may not matter to Apple, depending on exactly what the issues are, or how much of an advantage they extract from it.  The TBR approach is typically well suited to mobile implementations, and Apple may be happy to have their non-mobile solutions suffer in a few applications (especially niche) in order to have their mobile solutions be significantly better.  And it may also be a generational thing -- with increased degrees of SoC integration and improved processes in the future, the TBR architecture may be able to extract more value from that than IMR architectures.  Its a very complex problem and nigh impossible to predict how things will play out.  Having its own silicon allows Apple to be "different"... that doesn't always mean "better" (and "better" depends on the lens being used).