Remember, Apple chose PCIe 3.0 for the Mac Pro 2019 even though PCIe 4.0 was released in 2017. PCIe 3.0 was released in 2010.
Really not truthful. Apple did not design the CPU or PCH packages for the Mac Pro 2019. Intel did. So Intel choose PCI 3.0; not Apple. Apple just worked with the design decisions that Intel made.
Intel did not release a W-2xxx or W-3xxx class CPU package with PCI-e v4 until 2021. There is
NO WAY Apple could 'choose' something that was going to ship until
2021 in 2018-2019 when the Mac Pro
2019 had to be finalized.
What Apple shipped in 2019 is exactly what was a current Intel product in 2019.
The only relatively rapid adopter of PCI-e v4 was IBM ( Power Series and mainframes). There is a vast mulitple year gap where EVERYBODY in the PC industry did nothing. Intel , AMD , etc. It was not an 'Apple' thing at all.
Late 2019 AMD shipped some Eypc server processors with PCI-e v4.
www.anandtech.com
And the Threadripper 3000 series that was based off that core product set.
Pragmatically, those were not a real option for Apple.
1. AMD couldn't supply solutions for the rest of the 2019/2020 Apple product line. Forking Mac Pro off from the rest of the Mac line up was not that path that Apple was on. Especially, a year away from the transition off of x86_64 anyway! ( 2019 and the intel macs that slid into early 2020 were 'last gasp' x86_64 models. Not some new generation for the long term future. )
2. AMD over the 2013-2018 time span was relatively hostile to Thunderbolt. Thunderbolt was a key attribute of the Macs by 2017-18 when the design for Mac Pro would have been mostly laid down.
3. Back in 2016-18 AMD was just trying to keep the lights on. Yes, Apple was buying GPUs from them , but those were
not being crisply delivered on time. ( Remember the Mac Pro shipped with a relatively 'old' 580X as the basic card because there wasn't a newer viable alternative at that price point in AMD's line up. And the W5700 was a 'paper launch' for the MP in 2019... didn't show up until 2020. ) Doubling down on 'maybe AMD will pull it off' probably was not a notion that someone was willing to beat the farm on.
4. Threadripper had 'max' core count feature 'check box' , but it was not better at single threaded. It was very , very ,very much so a multiple user , multiple conncurent 'different programs' optimized chip than a workstation one. It fix some corner cases, single user wasn't the focus.
The line up was also short. 24 , 32 , 64 cores . And the 64 solution was a 2020 product also.
https://www.anandtech.com/show/15318/amds-64core-threadripper-3990x-3990-sd
[ AMD's high priority was shipping Eypc models , not TR ones]
Not that 64 would be useful since macOS has a 64 thread limit. So would likely not to turn off SMT for that model ( yet another mismatch in the systems design).
If Intel had delivered the W-3300 in late 2019 with decent thermals [ like probably most 2016-17 roadmaps said it was going to do.] then Apple probably would have taken it. Intel didn't. So the PCI-e v4 , 2019 option only happened in an alternative universe.
They highlighted the 2023 Mac Pro having 2x the PCIe bandwidth over the 2019.
Apple highlighted the theoretical bandwidth to the slots is higher. Apple didn't highlight at all cleanly what the actual backhaul bandwidth is to those slots.
None of the PCIe peripherals [other than SSD/NVme based 5.0 PCIe cards fully leverage 5.0] cited would need more than PCIe 3.0 to use since either they are Audio or Data Array only based cards.
But could you really get the PCI-e v3 on the six slots in the MP 2019 ( slot 2 , 4 , 5, 6-8) . The backhaul to six of the PCI-e v3 slots in the MP 2019 is just two x16 PCI-e v3 lane bundles. There is are two x16 , x8 , x4 and some MPX double x4s all attached to the back hual. If wanted to fill those two x16 slots and run them full blast the other stuff in slots 6-8 and any MPX connector used wouldn't have any bandwidth left.
The biggest miss [deliberate omission] was not supporting CXL 2.0 and folding that into their designs for the future.
CXL 2.0 largely is a band-aid to try to get what Apple has with their "Unified Memory" approach. It probably would be useful to have eventually for M-series, but back in 2017-2018 CXL wasn't the completely unified front it is now. Intel came up with the foundation of CXL and lots of vendors (including AMD) fought them on it before they submitted and got on board. AMD even delayed Zen 4 Eypc a bit to 'change horses' and get on board. But a small part of that though was Apple doing what they are doing. ( promoting the 'extra copying is bad' and leads to RAM purchase bloat movement. )